How to trace Fix tube guitar amp noise Hiss Harmony 415 Part 2 D-Lab Tek Tip

Part 2 complete. I spent the morning sifting thru the Harmony amp, seeking sources of noise. Found quite a few! Mainly, poor grounding and of course those corroded input jacks. Part 3 will show the MP3 input addition and hopefully the owner taking it for a spin. This has been a great project. Thank you all for your kind support. I'm doing my best with the time allowed. The donations have been a real blessing. Keeps the shelf's stocked and video rolling! More good stuff on the way..TD

[@vadenk4433]

When dimed the H415 has some of the best sounding cranked tube overdrive I’ve ever experienced. When you jumper the inputs & dime the amp, the overdrive/distortion is glorious. I’d recommend anybody who stumbles across one to snap it up if it’s under $600. Clean examples sell in the $800- $1200 range & this model doesn’t show up for sale very often. Ever once in a while you can still find these for sale in the $300-$600 range by people who aren’t aware of how great this amp really is, & are not aware of the sizable cult following this model has. The h415 came stock with Jensen C12R speakers- which by themselves can sell for $300 - $400 a pair. The C12R is a great low wattage speaker for anybody going after natural 60’s tube amp break up/ garage rock sounds. Every 1960’s Jensen speaker I’ve owned (10” & 12”) have a real old school rock n’ roll sound that I’ve not heard with other speakers. Don’t be fooled by the new Italian made “Jensen’s” as they DO NOT sound anything like the real deal, made in Chicago Jensen’s

[@audiotechlabs4650]

I thought pt.2 was more informative than pt.1! I thought, after seeing where you put those 100 ohm resis-a-taters on the 6 volt filament supply was smart! You had more restate on that end and it does the same job. Glad you raised the twisted sister filament wires up above the chassis, over the components and tube sockets. Good move Terry! I don't think you get enough credit for your knowledge and experience. You make "tronix" an art! Those news witchcraft jacks, my choice, were gorgeous. Fantastic upgrade on the whole service. Again the owner will be thrilled! I would be. Thanxz

[@d-labelectronics]

Thank you my friend.

[@jasonkirkham550]

After seeing this video, I hope people will understand why amp repair is not cheap. Great video Terry.

[@hpelisr]

Awesome work, wow I just happened to be on the tube and up came your video. Great tips, Thanks.

[@EricNusbaum]

Another great video Terry! My favorite EE/Audio channel on KZbin!

[@sideeffects9418]

Hi! Is there a reason for putting the 100ohm resistors at the last tube and not the start of the chain? Thanks for your videos!

[@michaelj.podlovics2246]

Really helpful video. Clear logic to your troubleshooting and the scope helps visualize the progress along the way. Rferencing this for troubleshooting my own amp - thanks D-Lab!

[@mattdixon333]

Loving these Guitar amp vids, Terry!

[@sincerelyyours7538]

Good one, Terry, I'll remember the tap test for noise issues. About the balancing resistors for the filament line; if I understood you correctly, you put them in to eliminate common-mode noise by floating the filament winding so neither side ties directly to ground, correct? Doesn't the B+ ground tie into the filament winding or is the filament winding isolated from the rest of the transformer? Also, how did you arrive at the 100 ohm values for those resistors? Sorry for these newbie questions, I'm still kinda new to tube gear. Thanks.

[@Finom1]

Thank you for your educational videos!!!

[@relaxvideomusic]

Hi, nice video! I bought Pioneer xs 300t and it has continuous hiss some more in one channel. No connections. I can get 50% less some in one position of volume potentiometer and 0 with 0 volume . Can you help? Please. Thanks

[@VintageProjectDE]

Awesome tip! Thanks for that! But I'll be honest: I came for the awesome Tek 935A scope that I spotted in the thumbnail ;)

[@d-labelectronics]

yes Sir, I really love this scope, its a keeper

[@Bigjoedo66]

Another great Video Terry!!

[@danielsaturnino5715]

Waiting for part 3 for that mp3 input! :)

[@johncunningham5435]

Good problem solving; "elimination one at a time eventually leads to victory".

[@bronyraur3]

Love your channel, I've been having many issues with my '65 Bassman recently. I took it in for volume loss issues last month and received it back, but noticed one of the tubes had some slight red-plating and the amp popped and hissed every now and again. The problem was mild, but I decided to pull the chasis to poke around with a wooden chopstick. Didn't find anything, so I cleaned the scratchy pots with contact spray, turned off the amp, unplugged it and turned the switches on for an overnight current purge. Came back the next day and the amp wouldn't even turn on. I was wondering if you had any ideas what the culprit could be? I'm considering taking it back to a repairman, but it's honestly beginning to become a money pit. Thanks for the informative videos - Jake

[@kenhaywood3124]

Another great vid. Thanks Terry!

[@1trailwalker]

Hi Terry These are two great videos , as always I have learned a lot from your videos!! Could you explain more about the filament wires with the two resistors at the end and how it relates to a three prong plug ? Should we just replace the plug with a new two prong that will only plug one way?? Thank You !!

[@PaulinTaegu]

The filament wires would have made 60Hz hum which is common. Since this is cathode biased, instead of putting the 2 balancing resistors at the input tube socket, I would have installed them at the output tubes and elevated the heater voltage by grounding them through the bias resistor. Twisting the wires and elevating the heaters voltage through the cathode bias resistor usually eliminates and 60Hz hum problems. Hiss and crackles are most often caused by old CC resistors. I had a feeling you would solve the problem by replacing some old resistors. ;^)

[@zulumax1]

What is the best way to track down a noisy resistor? Freeze spray? Tapping, pressure, signal tracer?

[@PaulinTaegu]

@@zulumax1 Tapping works. New resistors with a 1% tolerance are cheap, you could just replace all the 10-20% tolerance of old CC resistors feeding all the preamp tube plates for pennies and see if that eliminates the hiss immediately. You know how some techs will just shotgun replace all the old signal caps, all CC plate resistors could similarly be replaced for very little expense without even testing 1st, IMHO.

[@goodun6081]

Terry, at 8:20, you can see that the terminal strip which has the (formerly) Black Beauty capacitor tied to it at one end also has a rivet holding the center- tab of the terminal strip down to the chassis, which is used as a ground point. You can't trust those rivets! It's pretty much guaranteed to be oxidized at this point, some 40 years after it was built; and the brass cold-rivet tends to relax and loosen with time. You should solder that point, or perhaps even drill out the rivet and install a bolt in its place. I would have repaired and improved that ground and then grounded the capacitor to that same spot rather than soldering it to the chassis a couple of inches away. It kind of looks like bad form, especially for a ham radio operator! "A Wizard should know better!". Treebeard

[@d-labelectronics]

Hello, Thanks for the message. If you take a close look at that terminal board, you will see that the center mount post/terminal riveted to the chassis is not used for an electrical contact (unused tab). I soldered the new cap direct to chassis. So the integrity of that connection is not a concern. Take another peek. TD

[@pickholder6189]

What is in your audio test set box Terry? Dummy loads I take it. Can you perhaps publish a video on this unit. I would love to make one for my workshop,

[@viewer54322]

Same

[@audiotechlabs4650]

Terry built and showed this wonderful piece of test equipment in previous videos. Thanxz

[@goodun6081]

I was watching the video on my smartphone, it's a pretty small screen and so fine details can be tricky, especially with my old eyes. It did look to me as if there was something else out or to that ground tab, although it's hard to tell as your camera moves around quite a bit. Anyway, my apologies. Of course, no reason you couldn't have used that terminal strip for a ground as long as you dragged out your big soldering iron and soldered the tab to the chassis. I remember an exchange of comments with Brad the guitologist where I warned him about riveted grounds like that, especially on old Danelectro and Valco amplifiers, and he said he never had a problem with one. Then, a couple of KZbin videos later, he did indeed have a problem with one of those riveted ground connections!

[@fekkyb]

YOU THE MAN‼️🙂👍🏽

[@MrBritrider]

Hi Terry, I just love watching your videos even though I don’t fully understand what you’re talking about. You are entertaining. Have you ever thought about working on the amp that has been the poster child for having the notorious hiss, white noise etc., the Fender 68 Custom Deluxe Reverb? It’s a fantastic sounding amp providing all the glorious sounds that Fender amps are known for but the hiss kind of ruins the experience for a lot of us. Some place the blame on the negative feed back circuit some say cheap tubes I certainly don’t know what it is. I would love to see you with one on your bench and taking a stab at quieting it down. If you need a volunteer, I would let you work on mine! Thanks and keep making your entertaining and helpful videos.

[@d-labelectronics]

I'd be glad to take it on. Where are you located?

[@MrBritrider]

Terry, I'm located in Upstate NY.

[@andy-doublebarrelhouseband5686]

Awsome video!!

[@schreds8882]

Amp's looking good. 😀

[@d-labelectronics]

Hi Kris, I have e-mailed you twice about the amp, are you getting my e-mails? Are they going to your spam??

[@schreds8882]

Terry, I got your email on my gmail account so that works. I replied, yes to everything. 😀

[@sjirk]

thanks man! those videos really help.

[@RobertKohut]

Nice!!

[@cMaXeJIJIo]

Come on, feel the noise! 😆