Powering Up A Forgotten 60-Year-Old Tube Amp - Bogen Challenger CHB50

[@MrCarlsonsLab]

You're half way to stereo, now the owner just needs to find another. They're actually pretty easy to find too. Yes, your project would require a complete re-cap... ETC. When they work properly, they sound very good. That amp should be loud enough "with a good speaker" to get uncomfortable to be around, without too much distortion. The larger Bogen's with 8417 tubes were very powerful. I have many waiting for restoration.

[@hashtag-shaneiacs]

Some new restoration videos I hope Mr. Carlson!

[@mikemar42]

Ha! So cool to see you hanging out in the comments. I love it when two of my favorite smaller channels collaborate. You guys have both helped so many of us out here.

[@kevinwager9284]

Uncle Doug works wonders on these old amps

[@robertmartin6208]

Bad coupling capacitor allowing dc to pass through is probable cause of the red plating tube. I love tube amps....they sound great. Get it going!!😊

[@seansweeney3532]

Yep, but those 6L6 tubes look original RCA... SO just as likely needs new tubes. The Bogen stuff had typically great coupling caps, but this was after the buyout.

[@seansweeney3532]

Also he has no speaker load.

[@peleepunk1833]

I’ve had several of these they work great for guitar amp. Loud. Uncle Doug I think has done some of these.

[@Slane583]

I have one of these old Bogen PA amps. I got it from my step-mother in March of last year when she acquired an old legion building in town. It was part of what the original owners had setup for a PA system in the building and it was running into a 500watt amplified SUNN sound mixer. Mine is the bigger brother to this one, it is a CHB100. My parents were fixing up the building and the sound equipment wasn't required for their needs. So as a Bday gift my step-mother knew I was into old stereo equipment and said if I was interested in any of the gear I could have it. So I took the Bogen amp, the SUNN sound mixer, a small Realistic TM-150 AM/FM stereo tuner, compact Realistic cassette player and a pair of SONY APM-D4 speakers. Sadly I haven't found a use for the Bogen or the SUNN sound mixer and they've been riding around in my truck since then as I have no place to store them safely.

[@zulumax1]

On a unit like this I run a variac and a dim bulb together, if things start to short out the bulb will limit the current and alert you to the problem before the fuse blows or magic smoke appears.

[@briangoldberg4439]

dark spots on the side of the tubes is just getter. perfectly normal

[@b.powell3480]

That amp brings back memories!, I picked one up at a church bazaar ( similar to a yard sale) when I was in Jr. High, ( bought it cheap, from money i made mowing lawns). The mic inputs are those pld style amphenal screw on connectors, they look like bnc connectors on CB antennas. The mag connector is for a record player with a magnetic pickup and needle, great amp, i used mine until i was able to save enough to buy a Marantz receiver like the one you restored in the previous video. Just go through and replace caps, check solder connections and replace the tubes, have fun !😊

[@williambock1821]

These have the bones for fantastic guitar amps. I turned a Bogen Cha 33 into a Fender 5e3 that runs both 6v6 and 6l6. Put a new Hammond output xfrmr in it and all new guts. Turned out great!

[@westelaudio943]

Point-to-point wired amps are still being made today. PCBs were already around when this amp was made (I'm guessing early 60s?) but PTP is ALWAYS the better choice for tube gear - PCBs just don't handle the heat all too well. I have wired PTP amps all by myself and it isn't that hard, especially since tube circuitry in an amp is usually very simple. you just have to take no chances when it comes to possible shorts...

[@russellhltn1396]

The big problem with P2P is it drives up the labor costs (labor time) to build it. That's fine if you're building your own, not really practical if building to sell.

[@michaelszczys8316]

From tube socket to tube socket

[@jonathanhorne6503]

Redplating was from (probably) the leaking coupling caps feeding the 6L6 grids. Then shorted electrolytics. All that is easily fixable. These make great guitar amps or mono garage music amps

[@reinkansman1081]

You are a braver man than I. no need for me to see more. I had a guitar tube amp when I first started playing my electric guitar.

[@theoloutlaw]

You gotta have a go at this! You'll fall in love with tube gear as you learn more about how great the technology is. As others have said, the coupling capacitors have probably failed and leaking DC on the output tube. The bias resistor/cap, for the tube, may be out of speak and cap leaky. The filter cap (the can capacitor) is more than likely finished, and a good indication to the hum trouble even when the volumes are turned down. In other words, the capacitors all have to Go!! If they are not 'leaky', they are probably not operating and breaking down fast with the high voltage now, that's why it took a little time for them to react. If you got keen enough, you can remount new capacitors in those old shell capacitors just to keep it looking authentic, there are a few videos of people doing that you can youtube. The output tubes should be fine as you turned it off quickly and smartly. This is great old technology, please don't throw it, find it a good home if you don't want to bother with it. Oh and another incentive to learn and fix, there's a schematic available online! www.audioservicemanuals.com/b/bogen/bogen-chb/60815-bogen-chb-50-operating-manual Cheers, Rick

[@stphinkle]

Bogen is a brand that was more known for its school PA and Intercom systems. I wonder if that amplifier was used in a school, office, or something like that. The 70V line output for constant voltage speakers might indicate that. Some of those 70V line outputs were used to drive the in-ceiling or on-wall speakers found in schools, offices, hospitals, airports, malls, doctors offices, and other places used for background music, intercom, or paging. It is also possible that an amp like that was used for record players, tape decks, or brought around on a cart for announcements, or used in a small cafeteria stage or something.

[@robertdavis5714]

Nice production, as well only knowledge is Mr. Carlson. Yes, enjoyed seeing the red hot tube. Quite amazing you got sound out of that briefly.

[@robertmailhos8159]

That is a classic tube amp from back in the day Glad you are working on it

[@vida22aj]

I like that you now have a ESD Mat.

[@asn413]

i would enjoy seeing it recapped

[@vpconcepts9838]

I jumped out of my damn seat when you flipped the power switch and bounced to the music & high speed video. 😂🤣🤦‍♂️

[@kd1841]

Cool amp and great video. Reminds me of our console tube tv we had till I was in middle school. When I switched in on in a dark room u could see a slight glow from the back while the tubes warmed up. They were not red plating though, just a bunch of tubes giving off a little light. It was a Zenith. I thought I would die when the repair man had to take it into the shop one time because it required more of a repair than just a tube replacement. Thankfully he brought it back the next day and it marched on for several more years. 😊

[@timsterz1]

I'd like to see you work on it as I have one myself that I just haven't been able to get to yet. A pair of old mono PA amps like this can make a great old analog stereo set up or a single unit can be converted into a cool sounding guitar amp.

[@AudioElectronicsChicago]

Beautiful, get it going

[@Asriazh]

From what I know, you shouldn't even turn anything with Tubes on, without having all paper/wax capacitors replaced. They might still work marginally, but they could also fry stuff beyond repair and you'll have more work ahead than initially. Nice to see that kind of tech being worked on. Nothing you see every day! Thanks!

[@crashoverride328]

Yup, basically they stop being capacitors and become resistors. He mentioned watching Mr Carlson - he covers this issue quite frequently, I would suggest he watch a few more videos.

[@CDJF1]

You can if it's on a variac.

[@Asriazh]

@@CDJF1 yeah, you can, on a variac, having the ingoinf voltage way down. but then it's pointless, cause the tubes won't even conduct properly, and you can't check things. if you up the voltage enough for them to conduct, pretty much the same will happen that happened here: Fryage 😅

[@timsterz1]

Although I agree that the old caps will undoubtedly need to be replaced. In this situation where you're just trying to see if the entirety of the unit is still in tack, a variac brought up much slower than in was in this case, can often re-form the old caps enough to get you through an initial check to see if you at least have a working amp to begin with.

[@goodun2974]

@@CDJF1 , Personally I would not use a variac to power up an old tube amp in unknown condition without at least checking for bad/leaking filter caps and coupling caps, and preferably replacing the most likely failure points first, unless you also have a sensitive ammeter hooked up and can monitor current draw for signs of trouble. Ideally, a light bulb current limiter should be in series with the amp's power transformer. Otherwise you risk going from "Ah Fix It" mode to "I Wrecked It"!

[@michaelszczys8316]

I have exact thing only I believe mine is 100 watt model with 4 power tubes. The microphone levels are for the two weird microphone jacks on the back and the third knob controls the RCA jacks , one to one side and the other to the other side. The master controls them all. It has multiple speaker connections for anywhere from one or two speakers at 4 or 8 ohm and I believe the higher settings are for use in multiple speaker configurations such as a public address system. I remember a bowling alley near my house having one of these at their control desk for public address. I bought mine at a yard sale in 1977 and some time later found one like yours at an electronics store among used stuff and it started smoking when I tried powering it up so I took it back. I still have the 100 watt and used it for bass guitar and just amplifying a tape player for many years but now I have quit using it till I go through the capacitors. I don't want it to get hurt. I had a lot of amps but this is the only one I still have because my brother and his ' band ' friends didn't like this one as it had no effects. I also once had an older model Bogen Amp that was rated at 50 watts and I scrapped it when it started red- plating the 5U4. Wish I still had it ( probably capacitor shorting ) I could probably fix it now. My brother recently told me he found another of my ancient ' metal case ' tube amplifiers still in his basement.

[@pjimmbojimmbo1990]

Zenith used to call it "Handcrafted Chassis" before they switched to PCBs

[@gdownz1044]

Old School 👍 This piece reminds me of my Father's old 1960s Lafayette 236A integrated amplifier. It used to get HOT 🔥 But it sure sounded good. Wish I still had it.

[@paulboomer7109]

I had a bogan stereo receiver tube amp it had a third channel it would borrow a little from the left and a little from the right channel create the third channel there was no amplifier control whatever you put in for volume is what you got on the third channel this was 1964 it had a tuna that had two fuzzy blue light bars that would come together when you were centered on an FM stereo station don't remember the model I'm 77 now still listening to my vinyl great job fix that amp..

[@jeffberwick]

You should definitely restore this. Since you already mentioned Mr. Carlson's Lab, you have the best guide possible. Cap replacement will fix the red plate issue in all likelihood. The prime suspects are the coupling caps, which leak DC and ruin the bias point of the output stage. Just assume all caps except ceramic disks and micas are bad. You know the drill on the rest of the contact cleaning, pot cleaning etc. Good Luck! Please fix this! They don't make them any more. Lots of people would pay good money to convert this to a guitar amp. See D-Lab's KZbin channel for examples.

[@chatrkat]

I serviced several of those over the years as a field service tech for Muzak / Mood Media for over 30 years. Challenger was the economy line amp. Nothing fancy just a relatively reliable simple amp.

[@paulomeyer3900]

I believe that's something to learn - tube amps topology. I would like to see you fix the Bogen

[@joes3485]

By the way, a 6L6 was a metal envelope type of tube, which was the early introduction version of that tube type. They see considerable use in military applications where vibration may be severe and a metal tube holds up better. The 6L6GB/C versions with glass envelopes are better suited to consumer applications. This amp has 70.7V audio output capability for PA systems. The harmonic distortion is rated at 5% although at low volume levels would be much less. It might make a fair guitar amp as someone mentioned.

[@diymaster1121]

I am not the best at tube stuff either but i am learning. Anyways the red plating output tube can be because of the leaky paper capacitors, It was also probably overloading the output transformer since it was passing a lot of current. Paper capacitors can cause really bad damage in tube circuits, It can fry your output transformer or power transformer and then good luck finding a replacement.

[@tee-jaythestereo-bargainph2120]

Nice Job , what state are you located @ ?

[@skip1835]

Commenting before I've taken in the entire video - - that's PA amp - - 1st professional band I ever worked in back in the 60's used one - - I remember driving into Boston from Cape Cod to go buy it - - - I believe Bogan made the same basic amp in a 100 watt version that we later found out that we wished we had purchased over our 50 watt job. Ha! just remembered, we were running those "Altec" horns for PA Speakers - very efficient and were popular with club bands back in those days.

[@russellmueller8179]

Wow ,had two bogen amps from the late 50s,hooked them up to two Klipsch corner horns,and I'm telling you bro hang onto yer socks! These were made for PA systems hence the outputs you didn't know what for.they were for dispatch/ office as not to blast the secretary out of her seat,while the Warehouse/ plant floor could hear. If I remember rite ,those metal capped tubes marked bogen were actually a sort of filter caps ( good luck finding them) and may be your hum problem but more likely a ground point problem . That sounded more like ten years after to me , and you should play more.keep up the good work ,and keep working on the stuff that was built like a brick crapper!

[@mk23hk]

You plugged your cable into the Mag input. Which I believe is PHONO input. It would overdrive the circuit I believe. You should replace those caps asap! They are so old they are ticking time bombs if they are not bad already!

[@russellhltn1396]

Agree: MAG = Phono input.

[@goodun2974]

@@russellhltn1396 , It's probably a ceramic cartridge phono input and not a magnetic cartridge phono input, and therefore it wouldn't have any bassboost equalization or additional gain like you'd expect for a more modern phono input stage. It still would probably overload a little too easily with the input level from a magnetic guitar pick up.

[@russellhltn1396]

@@goodun2974 To make it usable as a guitar amp, it's going to take some modification. But not a lot.

[@goodun2974]

@@russellhltn1396 , Terry Kath, original guitarist for Chicago, played through a Bogen PA amp, purportedly mostly in stock condition. He got a killer tone from it!

[@michaelszczys8316]

I have 100 watt model, bought in 1977 and used the hell out of it. It's been sitting for last 20 years and now I'm afraid to power it up without changing capacitors. People say they make great guitar amps but the only reason I still have it is because my brother and his ' band ' friends didn't like to use it. They stole or burned up everything else I had. This is the only one left. One of its best uses was trusted friend ( he would bring it back ) would borrow it , a heavy speaker, and tape player to take to parties, put in the middle of the house, and play Live Ramones tapes. If it could hold up to the Ramones, it could handle anything.

[@mikecampbell5856]

My son has two of these in great condition. He used to use them with his computer with some Infinity speakers. He liked the contrast of old and new. In the 70s when I was in the Navy, all the communications gear I worked on was tubes. I once got 450 B+ plate voltage from a transmitter through my chest. Wow, did that hurt! I was sore for days. Be careful! I want you to fix it for selfish reasons. One of his amps has some hum and I want to learn from you how to fix it.

[@foobarmaximus3506]

Man, this looks like so so much fun! It also looks scary. Long ago when I worked at NASA, I had a little office with a bunch of old equipment and scopes and stuff. I was always playing around and smoking equipment and tinkering. That's because I was a software engineer and I was supposed to be writing code! Heh. My office was full of super cool stuff though. So what did they expect? I like the old electronics. Most of the problems I found back then was related to what I call "stank tube". Haha! You obviously found one here. Great video, as always! Watch your fingers.

[@robertwear1675]

As others have stated this is a PA amp probably used for an office system for background music and public address due to the mic input. When using a microphone the other inputs were probably muted. Watch out for the death capacitor. The plug is not polarized and when plugged in the wrong way there could be many deadly volts on the chassis.

[@jeffberwick]

A couple of comments on the 6L6 power tubes: at 2:49 you mentioned that he tubes looked "smoky on the sides", but you may have figured out that's OK. The smoky part is just the getter, which in this case was flashed onto the side of the glass instead of the top. Most tubes have a top getter, which is a darkened shiny region of a reactive metal that absorbs impurities to prevent gas and contamination in the vacuum envelope. But some tubes have this getter on the bottom or the sides. The side getter looks kind of reddish and smoky, but it's not bad unless it turns white due to exposure to air. The other comment is that at 11:23, when you pulled on the glass and separated it from the base, that's not necessarily the end of life. In your case the tube was probably bad anyway, but if you actually broke the glass stem at the bottom of the base, you would have seen a very white getter. Hard to tell from the video whether your tube is just dirty or actually went white. If you are curious, you can carefully cut the bakelite base apart to see how the stem comes to a point at the bottom.

[@russellmueller8179]

Good advice,did you know you can make breakfast on one these?t God bless simple class A stuff. I remember the first time I tried lifting one of these.was pretty sure it was welded to the floor but 200 w x2 bogens equals Nirvana. The amps went on for guitar and keyboard use.wish I still had them If you noticed these amps clipped a lot softer than ss stuff and made the great guitar amps.i don't think there would be rock n roll without them. Keep on trucking!

[@tomsherwood4650]

I once got a CHB 35 amp cheap and I converted the front end preamp stage from the Bogen plan to identical to a Fender input stage. Then I installed hookups for guitar. If I get it back I will use one of the extra inputs to try to make a reverb channel with a spring job. The only issue is the output tubes. IF they ever go bad, it is mod time or search out expensive identical tubes.

[@ghostexits]

I’ve often wondered if there is some electronic advantage to the chaotic wiring style one finds in most American point-to-point wired tube/electronic assemblies. If you look at UK/European electronics from the same time, you see a very different p2p wiring style.

[@joes3485]

In the case of the all-glass smaller tubes, note there is a gap between the pins at the bottom of the tube. When viewing under the chassis, the first pin in a clockwise direction from the gap is pin !.

[@watchtheskies]

The one thing I know about tube amps is that you must always have a speaker attached or at least a load of the correct impedance or bad things will happen

[@williambock1821]

The difference between point to point and PCB’s is this will be running long after you’re dead as long as you keep the electrolytics up to date. Solid state gear is made to break a week after the warranty is up.

[@charleslambiase5670]

That was my first ever bass guitar amplifier that I used to play out with,, it was given to me by my father and Uncle it came out of the school auditorium that I went to school with when I was a kid,, I got it when I was around 13 years old,, I bought the adapter turn it to quarter inch we screwed it all in the back I would blow through 6l6 tubes like crazy but that was the sound..

[@greggorr314]

Three cheers for amplicorn!

[@russellhltn1396]

Why some people are afraid of solid state: 1) It's different 2) It's unforgiving. Make a single mistake shorting something out, and the transistors are fried. Tubes are generally forgiving, they'll handle a temporary overload.

[@mantolaman]

This one reminds me of my old Bogen RT8000 that I've paid to have recapped, but it's still got issues. I'd be glad for you to have it if you want to pay the freight on it? It's been collecting dust for a couple of years now.

[@Earcandy73]

Time for a full recap. Always be sure to use a dim bulb tester while bringing up the voltage. I don’t think you gave it enough time for the filter caps to reform.The wax caps should be replaced anyway.

[@oxfamshop]

When you mentioned the high voltage I imagine it will run hot . A friend of mine had a Class A component HIFI the power amplifer used to run very hot . He needed to have a seperate ring main to cope with the power draw of the system

[@MichaelYates]

Like you know nothing about tube amps, I would have been just a shocked as you was when it all started to go wrong. Great Video

[@terrym1065]

It's really up to you and the owner moving forward bro. If there is a need for repair/restoration go for it, otherwise use it to educate yourself on tube equipment. Careful experimentation is called for of course. Modern circuit boards are much more friendly...

[@srtamplification]

You should always check for shorts on the power transformer and condition of fuse before ever applying any voltage. Bringing tube gear up slowly on a Variac is smart, but without anyway to monitor current, it is not really showing you anything, you should either have a ammeter to monitor as you are brining it up so you can shut it down when the current starts going crazy or have the dim bulb in series with the variac and load to limit the current. Also, those electorlytic caps need to all be replaced. The negative bias is something that needs to be checked as well. This could make a great guitar amp if restored and some mods made.

[@AN-ce1nd]

They were used in department stores etc. Bogen is typically a company that specialized in that type of market.

[@dannyfreitas2120]

If you power it up. Put a resistor on out put. Many people blow there output transformers

[@spacemissing]

It's a PA amplifier, not a hifi amplifier. It probably doesn't have good response above 10 kC (10 kHz). The controls are designed for mixing multiple signals or fading from one source to another. Tubes are easy to understand. Relative to transistors, the grid functions like the base (bipolar) or gate (FET); the cathode functions like the emitter (bipolar) or source (FET); and the plate functions like the collector (bipolar) or drain (FET). A GB tube will be OK as a sub for a GC unless the plate voltage is too high. Get a reprint of the RCA RC-30 tube manual. It will help you a lot.

[@russellhltn1396]

When bringing up old tube gear, you need to monitor the current draw. That's why many use a "dim bulb" (including Mr. Carlson). The bulb will act as an automatic current limiter. With that, you would have known something was wrong long before the tube red plated. Also: always have a load on the speaker output. Some amps will self-destruct if they don't have a load. I wasn't able to see if you had a load when you first turned it on.

[@dougmcdonald300]

Cool vids but did you record the audio to cassette tape. Needs the dolby nr turned on 😉

[@oliverisailovic]

You are a very brave fellow. It is risky to include such an old device without basic measurement. That 6L6 glows probably because the other one is not working. I advise that you first replace ALL the old capacitors and somehow check the tubes or replace them with correct ones. Next is the high voltage and bias check. Otherwise, something can catch fire or explode and hurt you. The capacitors on the grids 6L6 that connect to the phase inverter are especially important. If DC voltage "leaks" through them, the output tubes will be fried. And maybe the output transformer. The configuration of that amplifier is ideal to make a guitar amplifier out of it. Something similar to the Fender Bassman 50W. Someone who plays the guitar would be overjoyed with that. Be careful dude!!!

[@joes3485]

Chances are that the tube which shed its glass envelope did so due to the red-plating of that tube multiple times. Most of these output tubes (the 6L6GAor B) can hold up to short duration red plating, but don't push your luck. The underlying cause in this case is probably a shorted or leaky .1mF coupling capacitor to the signal grid of that tube. The signal grid of a 6L6 tube is pin 5. The way you read the pin-outs of tubes is from the bottom, look for the keying bump on the center black plastic pin of the tube. Count pins from the bottom in a clockwise direction from that bump or key. You should see two 100K ohm 1/2W resistors each going to pin 5 of each 6L6 tube. You will find that there is also a .1mF capacitor connected to pin 5 of each tube. The one that red-plated likely is either shorted or leaky. Change that part and you may be able to get it running without red-plating. There is supposed to be a negative bias voltage of -45VDC going to the junction of those two 100K ohm resistors. Check for that voltage and if it is low look at the 20mF @ 50VDC rated capacitor in the power supply. Get the negative bias right before keeping the amp on very long.

[@jimcabezola3051]

This sounds like a nice subject for research into the design philosophy of mono Amp design in the late 1950s. Read up on it, yes. See how they did it in MY day. Don't risk your health and well-being for it, though. You are more valued by us than this inanimate object. If you like, clean it up cosmetically and let it shine on a nice, safe display shelf. Enjoy that. Enjoy your continued, non-electrocuted life! 👍 We look forward to more videos from you.

[@rickg8015]

There is really good Point-to-point hardwired and not so good rat’s nest type Point-to-point hardwired..

[@dhelton40]

Well if you could find a second one you could have stereo. This was a budget model, it has high z mic inputs with no provision for low z transformers (which better PA amps had). I would replace the cannon screw on mic connectors with 1/4 jacks. The center off aux input was really to save on a slide switch, and in most applications it was seldom used. These unit were used in church lecturns and restaurants for paging and background music. The mic cable could not be more than about 15 feet (high z) and perhaps a Muzak fm sca decoder for music. The distortion you hear, may well turn out to be bad output tubes, remember that unlike transistors, tubes die a slow death and as they age, can start to sound awful. I would recap the whole thing and also remember that carbon resisitors can drift with age too...check the bias

[@doug4bears]

Hey AH....love your show. Do you ever work on Realistic stereos?

[@59seank]

Needs more corn.

[@jamiboothe]

Change out the caps. They are easy to get to. Clean and refit all the sockets and clean the pots. Then check for red plating. If red plating has vanished, then rebias and check on the O scope. I bet you a dollar there is nothing else wrong with the amp. Except a couple of resistors that may have drifted high.

[@justicelut]

Red plating is a classic sign of capacitor failure. Especially electrolytic!

[@ArthurJS123]

Bogen equipment was more for public address (PA), as opposed to home audio/hi fi.

[@roncarter2188]

People have a lot of weird conceptions about what to do what not to do if something is old and has old capacitors in it, if you dont have knowledge of electronics its best to get educated. So you did the right thing by dialing it up slowly on a variac, if it starts to hum real loud turn it off you're not going to hurt anything, you change the capacitors out done deal. No harm done and my experiences has been most of the time they actually will work right off the bat, put an input in where the microphone input is for guitar and enjoy.

[@skullheadwater9839]

6L6's were invented in the 30's. Originally, they were designated just 6L6 and they were in a glass envelope which was encased inside a black metal can. Eventually, they put they in glass bottles the first was the 6L6G which was the coke bottle shaped tube. Later these would be made in standard shaped glass and called 6L6GA. Next came 6L6GB and finally 6L6GC. In short, they have different spec as time went on their ability to handle higher voltage and current as well as drawing more filament current and therefore had higher output. You have to be careful putting an earlier version in later amps designed for later 6L6GC's because the amp will be biased for the more powerful versions, could have more voltage than an earlier one should be exposed to and could potentially damage your tube if left in this situation.

[@ohmbug10]

It would be nice to see that Bogen working again but that's easy for me to say when it's not on my coin. I'm going to guess that a capacitor shorted to make that tube red plate.

[@gameyord7182]

15:13 the GC is a storage and/or fabrication designation,as long as it isnt another tube it will be just fine (in my experience) But looking at the minature it didn't went very well for you

[@andydelle4509]

Just a little primer here on AC induction motors like your fan at 150volts example. AC induction motors always run at slightly less than a multiple of 60hz, 1725 or 3450rpm. Changing AC voltage does not change the speed, well not in theory. What varying the voltage does is to vary the torque. So while a fan for example wants to run at 1725 or 3450rpm even at say 70 volts AC, the weakened torque does not overcome the air resistance as well as at full power. Therefore it slows down. But again the lower AC voltage is not lowering the speed directly. It's lowering the torque. So while varying the AC voltage can ultimately vary the motor speed, it's highly sensitive to the mechanical load and very sloppy speed regulation only good for things like fans. This is why VFD, Variable Frequency Drives, are used today for AC motor speed control. By electronically varying the frequency, you get true speed control at full torque.

[@michaelkiley1192]

When a letter suffix is added to a tube number, it means that an improvement was made to later production of that type. When the 6L6 (metal) and 6L6G (coke bottle glass) came out in the 1930's, they could only take 360 volts B+ and had a plate dissipation of 19 watts. Over the years, they were upgraded to 6L6GA, 6L6GB, and finally, 6L6GC in the late 1950's. The 6L6GC could take 500 volts on the plate and plate dissipate 30 watts. Therefore, it is ok to replace lower letter suffix tubes with higher letter ones, but NEVER put lower letter suffix tubes in sockets which specify higher letter (later) types.

[@foobarmaximus3506]

Stand back from that thing when you power it up! If you turn it up all the way and hit the power, it might create a temporal distortion field and transport you back to 1955. Hehe.

[@envisionelectronics]

I’m confused by your “variac” with a DC volt meter. Is it rectified before going into the meter?

[@russellhltn1396]

That would explain why it was so slow to react to turning the voltage down.

[@joesimon2018]

Basically it's a PA amp with a pair of 6V6 in push/pull for around 20 watts. It's audio but mono so either find another one to make a stereo amp or mod it for guitar.

[@j.r.tumbleweed262]

I have a studio standard Fisher CA 800 I turned it up a little too loud and it just quit playing I have checked all the fuses I have owned out the Capacitor everything checks good. Do you have any suggestions Thanks.

[@rickg8015]

You could practice with this mono integrated amp in restoring tube gear.. A resto-mod may be in order..

[@steveishere7909]

Good rule of thumb, If the amp has been sitting that long just go ahead and replace those Caps. Nothing worse than taking out a transformer. (Especially The Can)

[@tomj4506]

This is actually a PA amp. Bogen was probably the biggest PA seller in the US. PCB's & tubes dont mix !!! Just too damn hot. Once I pulled a horz output tube out of a GE TV & the socket came with it !! Zenith was the last to hand wire. That went away through the 70's. Probably why so many survived til now. Red plate usually from leaky coupling cap to the G-1 of the 6L6's. Thats what killed the old one. 6L6 like other big audio tubes are stupid $$$ now so watch out ! LFOD ! Zeno

[@dont-want-no-wrench]

this experience should motivate you to read up on tube circuits. there are things you need to know.

[@scratchback2001]

Point to Point wiring leaves printed circuit boards for dead. It is also coming back in a big way.

[@foobarmaximus3506]

Technically, that was Maize. These old amps were powered by hamster wheels, and - they had to eat. Otherwise they wouldn't run. Someone probably took out the wheel long ago. And the hamster? He went to work for Marantz. Hahahahah!

[@hardball107]

Change out those old electrolytic caps asap, the big orange ones. That's where that hum comes from. Bad coupling caps are most likely causing the red plating, they will need to have the bias set and mismatched output tubes are not always a bad thing. They are never any good don't be surprised if you have to change all the caps. Talk to the owner, IMHO you should do a restoration and convert it to a guitar amp. A 50 watt, 6L6 powered, hard wired amp is worth a good chunk of money. Go to D-Lab on KZbin, send Terry an email about it, he might even buy it off you. If not I'll buy it. A converted amp like that can sell for up to $400 or even higher. Bogen was a very good name back in the day and just the fact it's has sound means all the expansive parts are working.

[@AHFixIt]

The owner ended up giving it to me and I'm currently working on a guitar amp conversion with new tubes! Video to come in the following weeks

[@hardball107]

@@AHFixIt Awesome, you won't regret it.

[@kennyh5083]

@@AHFixIt GB = Glass Bottle

[@frnkbooth6871]

Red hot plate is indicative of no bias on the output tube. It can be caused by a shorted grid drive cap. Grids are set to be negative voltage under normal operating conditions. Get a schematic and check it out. Not that difficult. Watch a video on basics of tube operation. No. The tube is likely not bad. You turned it off quick enough. Additionally, this problem was indicated by the distortion prior to the failure. Improper tube bias. Likely because of the leaking cap.

[@goodun2974]

Not only do printed circuit boards used for tube circuitry tend to fail from heat (solder joints break down, foils fall off, and poorl located or inadequate components get baked and fail prematurely) but *the board material can become electrically conductive*! Marshall, for example,, built thousands of guitar amps with this problem, and the conductivity between foil conductors caused overheated, burned-out tubes and transformers, and sometimes even electrical arcing and burning. It is possible to design circuit boards for reliable performance in tube amps, , but high-quality, "best practices" board design and layout are rarely seen in tube amps. Modern Fender amps also have terrible flimsy circuit boards with crappy leadfree soldering that breaks down in just a few years, as well as hot-running resistors and diodes that should have been elevated above the board but instead are pushed right against it so that they can overheat and sometimes even burn the board. Not to mention their use of shitty filter caps that fail prematurely. Again, it's possible to use circuit boards in a good design if you do everything right but most manufacturers just don't bother. "Eyelet" or "Turret" boards are a better choice for longevity and serviceability (and easier to modify for different or better tone) but they can't be stuffed with parts by robots and therefore require a lot of hand labor to build, hence a higher cost to the end user.

[@partylee007]

You probably should have run it through the car wash first. I would suggest the $10 ultra wash with the blow dry and the carnauba wax before you even take it to your workbench.😂

[@michaelszczys8316]

You must have watched ' Shango ' the TV repairman videos where he actually did just that with an extremely filthy color TV chassis.

[@partylee007]

@@michaelszczys8316 no, I watched the guy who made this video take a Marantz receiver over to the car wash and spray it off and then he shake-n-baked it in the oven to dry it out, but it turned out good. He got it working again. It was pretty funny at the car wash scene, seeing him hit it with the sprayer.

[@michaelszczys8316]

@@partylee007 ' Shango ' is great to watch. It was indeed kind of crazy car washing a chassis but it was really bad with rat crap and all. They didn't show the actual washing.

[@multimood]

probably would make a good guitar amp

[@francisigooch5269]

I don’t understand why you put power on before cleaning it up and changing the capacitors. You most probably have been pleasantly surprised

[@michaelszczys8316]

My 100 watt is probably fine, but after sitting 20 years I'm afraid to power up without checking capacitors. Don't want to hurt my old friend.

[@timmooney7528]

Fix it. Consult someone like Terry at D-Lab or Uncle Doiug for troubleshooting tips.

[@zulumax1]

A 6L6GB can only handle 360 volts max, whereas a 6L6GC can handle 500 volts max on the plate. The 6L6GB is also only around 19 watts compared to 30 watts of the 6L6GC.

[@goodun2974]

The original 6L6 (metal) and 6L6G/6L6GA were rated at 19 watts and 300 or 350? V. The 6L6GB is equivalent to the 5881 and those are both rated for 430 or 440? V at 23 W. Bogen circuits generally didn't push tubes really hard so that they would last a long time in commercial applications. It might be possible to use the lower rated 6L6 GB or 5881 in this amp safely but one would have to check with the B plus is at when plugged into modern wall sockets that deliver higher AC voltage than was common when this amp was manufactured.

[@tkmhurter]

I think it is worth to restore as a guitar amplifier.

[@hoobsgroove]

Do not hold the chassis with both your hands dangerous and lethal!!! Can't leave any capacitors in there, and resistors need to be checked for value. The other power tube is dead as well You can burn out the transformer when red plaiting

[@russellhltn1396]

I would agree with you that there's not much use for an old PA amp. However, someone might like to turn it into a tube guitar amp (those are still a thing). Check out "The Guitologist" channel as he's done a few conversions like that.

[@trevornmartinmartin2756]

i would love to own this

[@skullheadwater9839]

PCBs are not great for a tube amp, too much voltage and amperage. I get it that it is cheaper to have a machine make a board with all of the components soldered on, so you don't have to have people that know what they are doing, cheaper etc. Tube amps with PCB's, the board eventually goes conductive. The board is a fibrous material which small metallic hairs can grow in like blades of grass across bridge across traces because, as you know, electricity passing through a conductor causes a magnetic field. This can cause direct shorts as well as bias problems. Once your board is fried there's three options. Replace the board which usually costs as much as a used amp, re-work the amp so it is point to point as it should have been in the first place or throw the amp away and buy a new one. P2P tube amps can be endlessly repaired, just unsolder the faulty component(s) which you can easily trace visually what it hooks up to. This is why many vintage tube amps which are up to 70 to 80 years old can be endlessly repaired cheaply by swapping faulty caps or resistors. Even the tube sockets are board mounted in most modern tube amps which can damage boards with the shear heat. PCBs are best left to solid state.

[@jimcatanzaro7808]

Tube amplifier repair isn’t that hard I always replace the caps after I have tested the power supply transformer and inspect any burnt resistors and I test the tubes then clean the tube sockets before I bring it up on a adjustable transformer Then I clean all the pots with deoxit And if a fuse is blown I would definitely take all the tubes out and bring it to 50vac to see that the dc voltage after the rectifier and always get the schematic so you can check your voltage and bias on the cathodes

[@michaelowens944]

I still remember when a radio or TV stopped working right during the late 50's early 60's taking all of the tube out and going to the drug store and checking them in a machine. You could buy new ones there and replacing them. Usually fixed the problem. Simple stupid but very dangerous on the TV's'

[@larryh.4629]

Yeah remember my dad getting knocked across the room in his TV repair attempt he had done it successfully several times before but that cured him and he never poked around in a TV again. Who says you can't teach an old dog.lol.