How to repair KT-88 tube stereo mono block amp Dynaco MKIII D-lab electronics

Just finished repairing a nice set of Dynaco mono blocks. these are great quality units. My Dad ran a set of these back in the day. Vintage tube amps are the way to go. Hope you like the video.

[@jamesbracken4618]

I notice there are 14 thumbs down, I don' t know for any reason why anyone wouldn't like what you are doing on these videos, I absolutely love what you're doing. I've learned so much from you. Thank you so much for showing me the right way to work on amplifiers. Keep it up. GOD BLESS YOU! GOD BLESS AMERICA!! GLORY BE TO TO GOD!!!

[@Geopholus]

Beautiful video, everything done right. Personally I always replace ungrounded AC chords with 3 wire grounded plugs, and eliminate ground loops other ways if they present a problem, but otherwise I really appreciate Your methodical application of common sense with good electronics theory, and demonstration on using a varian to avoid problems, rather than certain other YT channels who, early on, detect problems and then go ahead and turn up the Variac all the way, with no regard to ruining transformers, tubes,... etc.!

[@dylan-reece]

Awesome Terry! just happen to have a pair on my bench this week. Great info. Thanks my good man.

[@johngerson7335]

Always enjoyable to watch you work tube amp circuits Terry. As the old expression goes : You flat got it!

[@kenhancock8931]

OH man what a sweet set of mono blocks! sux about the tubes. crazy how it was two and not just 1. Exellent as always!!!

[@jjiacobucci]

Hi Terry! Another awesome video. You're the man! Super step by step examination of the Mark III's.

[@whatsstefon]

Shame about the defective tubes. :( What a show-stopper. I had a similar issue a few months ago while restoring a '75 Fender Bassman 50. Opened the box of matched duo of 6L6GC tubes (Tung Sol) and one had a crack in the glass. I noticed immediately due to the getter being not so nice and milky. Had to order a new set, and now the amp is humming along at all the gigs I play it at. I was lucky to have the supplier replace them. I've had some 12AX7's have a nice straight line crack in them when I open them at the supplier. Now every time I buy them in person, I inspect them in front of the sales guy at the wholesaler I purchase them from.

[@johnsimoes2172]

Great video Terry as a footnote I had a bad pair of genolex Kt88 a few yrs back restoring a west guitar amp with dynaco transformers . The loudest and heaviest combo amp ever

[@keithnelson5605]

Really enjoying the audio gear videos. I have some Dynacos that need refurbishing. I'll be looking back at this!

[@greggaieck4808]

D lab Electronics your utube videos are awesome

[@RobertKohut]

Nice! Great examples of a pair of Dynacos. Not often you find them so nice, never mind a matching set like that!! A great score for somebody!! I have seen many for sale as "pairs" but they are from different years and were never exactly the same as each other.

[@Finom1]

Thank you for the details Terry!!!

[@flintdavis2]

, I don’t know if it’s a big deal or not but seeing those wires passed thru those sharp sheet metal holes sticks in my craw.

[@69mercurycyclone44]

Great video as always! Hope they replaced the tubes. Love your work and wit!

[@pneumatic00]

Those Dynas are in quite incredible stock condition. Two brand new tubes, two open heaters? Yeah, I would be stunned, too.

[@akkudakkupl]

Brand new, dropped once.

[@jordanrenaud-pq7rx]

Good vid! Now i need to borrow a Variac and Scope to restore my MKIII amps.

[@wadehicks9270]

You do excellent work Sir.👍👍👍👍👍👍👍👍

[@greggaieck4808]

D lab Electronics your friend Dynaco Amp is so awesome

[@frankgeeraerts6243]

Penthode and triode in same tube envelop.........penthode voltage amplifier direct coupled to concertina triode.......only one stage coupling capacitors, good sounding recipe up til today.

[@neil6765]

I love watching your videos.

[@waynetoneseekerandersen2213]

in regards to grounding... 3 prong... you could suggest they plug them into a gfci receptacle for life protection. Thanks Terry

[@mobicus1]

So , a matched quad of tubes, huh? Not so much , it seems . Maybe 2 matched sets of 2 each, with one set needing a garbage can. This is why I take vendor claims of tube matching with a grain of salt and nothing more . Great video as always !

[@kerryg4119]

That is a really clean pair of MKIII's. I'm running a pair of MKIII clones I built using Triode Electronics transformers and Gold Lions. I use them to push the low end on my bi-amped system. I use a Dyna ST70 on the top end. For what those Gold Lions cost, I'm surprised that you got two bad ones in a matched quad. They must of been damaged after the match testing. Interesting that you just happened to get lucky picking two good ones for the first amp and got the two bad ones together for the second. Sounds like my kind of luck!

[@djvartan]

Great video

[@normjacques6853]

Hi Terry! I'm really enjoying your videos...especially this one, since I have a soft spot for old Dynaco kits! :-) With regard to soldering to a chrome-plated chassis: Try this - Get out your trusty Dremel tool and install one of those little (1/4" more or less) conical green grinding stones. Right where the twisted lug meets the chassis, gently grind yourself about an 1/8" dia. rough spot...without leaning on the Dremel too heavily. Just enough to break through the plating. Then, hit it with a small dab, or drop, of flux, and solder away!! BTW, you are the only other person I know of that uses a Beckman multimeter!! The way you approach these projects, I suspect that you're military trained (I'm an ex-Navy avionics tech - '69-'72). Thanks for the great videos!

[@normjacques6853]

Also...What is that audio test set you have? Make/model?? Thanks!

[@wadehicks9270]

Norm Jacques thank you for serving our country Sir.

[@swinde]

17:47 ... This "bias" reading is derived from the voltage drop across the common cathode resistor 11.2 ohm, 1 watt. The line voltage will not be a factor in the setting. Dynaco did this so hobbyist could use any DC meter and first measure a new standard "D" flashlight cell and then set the bias to match the reading of the battery. The new D cells would measure 1.56 volts on a calibrated meter so they are used as a reference here.

[@larryshaver3568]

A friend of ours had two mono dynaco power amps on his his system even after he replaced the old preamp with a pat-4

[@crbielert]

beautiful.

[@dhpbear2]

Terry, It'd be good to see how these amps perform using a square wave (rather than a sine wave). Especially when checking tone controls. Those amps are in GREAT condition. No pitting on either chassis!' Also, I've heard that adjusting the bias (using a sine wave adjusted for low-level output) for no cross-over distortion (plus a 2-3mA safety margin) resulting in less bias and longer output tube life.

[@wheeler2581]

are you half in the bag when you do these video's ? i am LOL! great video's very informative.

[@antoniograncino3506]

Ah, but you CAN solder the can lugs to the chassis: merely scrape off the chrome plating under the twisted lug, down to the base steel, and use at least a 60 watt iron and a little additional rosin flux on the work and yer golden. BTW: sure sounds to me at 5:22 that he said "rectumfier tube"

[@russellhltn1396]

Strange about the filament. Did you look at the base inside the glass? I'm wondering if a spot weld let go.

[@steveeolio]

pardon me kind sir ... i have a conn stereo amp from an old organ ..it had a 12 inch alnico speaker on one side and a 4 inch silly filed coil speaker on the other side i verified the function of the channel with the 4 inch speaker by disconecting the voice coil wires and connecting another 12 inch speaker .. sounds gr8 .. my question is the field coil has a 5000 ohm load with a black yellow and red wire im assuming the black is a ground and the red and yellow are powering the field coil... how would i put a replacement load on the field coil circuit to avoid future problems with the transformer that provides power to that electromagnet.. i assume a 5000 oh power resister of 20 watts or so but my confusion lies in 3 wires!the amp is push pull stereo with 12v6's as power tubes ( massive power trans ) lovely sounding amp that i want to use as home stereo unit..

[@jordankashuba3467]

I have a Dynaco Power 400 solid state power amplifier with the Dynaco Pat 5 pre-amp and matching 22 band EQ powering a set of Klipshe La Scala 15" corner horns on chanel A and a set of sealed speakers with a 10" and a 12"" front firing woofer in each the same tweets, a little smaller mid-horn than the la scalas on chanel B. I cooked something in the power amp a decade ago and I only have left side working now. I need to find out whats toast(transistor Im guessing).and I should switch out all the caps. My dad built 3 of these as kits back in the 70s, mine,my cousins and my uncles. I have new harmon kardon with powered sub and polk towers now and my current system doesnt even hold a candle to that old Dynaco. Where can I order parts for this old beast?

[@wesleymatthews137]

Hi Terry. I noticed you didn’t determine the foil end of the orange drops before installing them. Or did you off camera? I would think in HiFi audio, it would make a difference? What are your thoughts on that?

[@carlburgess9635]

So Terry, did the source of the tubes compensate you, what ever, could you let us know where you got them, so we know if we should use then? Carl

[@zulumax1]

By the way if you run a tube that has gone to air you will damage your power transformer in a jiffy. Look for a milky colored getter spot on the tube, it should be silver like a mirror and turn white around the edges as the material is used up with age like the old tubes shown here, but not all white.

[@douro20]

I wonder if anyone has built amplifiers with 3c22 disc seal triodes? I've read they are similar to 6550s but need forced air cooling above 60w power dissipation.

[@pinterelectric]

Sweet

[@rciancia]

What a shame.. those Gold Lions look brand new.. someone goofed on those tubes - whoever bought them got ripped off. Nice job on those amps... Perfection - Ron

[@ryanfenelon657]

Ron C I believe they were reissues right?

[@gsmith160]

YES, those are New Sensor Russian '88's... I have them in my Mark 3's, tried the Electro Hamonix re-issues (Russian), only lasted about 1.5 years of weekend use. The New Sensor lasted 6 years! So, on my second matched quad of Genelex...

[@williamsquires3070]

(@12:05) - those output tubes look a little gassy to me. Also, I see a Heathkit! The blue case with the storage compartment gives it away. 😎

[@jordanrenaud-pq7rx]

i do not have the Dynaco pre amp for my MK 111 amps. Do i need to short out certain pins on the female preamp power supply output at the backs of these amps so i can just connect another preamp to their inputs? Or simply leave everything stock? thanks very much sir.

[@zulumax1]

I have matched quad set of the Russian made Genalex Gold Lion KT66 in my Heathkit W5M mono blocks running now with no issues. I had a bad reliability problem with the Russian made 6L6G Tung-Sol 500v plate Coke bottle tubes going to air many times, would not recommend them.

[@jordanrenaud-pq7rx]

bit late now, but Do you have the black lead of your multimeter connected to ground during the bias readings? I can see that the positive lead is connected to the bias pin coming out of the power socket for the pre-amp. Thanks.

[@jordanrenaud-pq7rx]

hi. Where can i purchase a set of those new filter cap cans. What is the specs on them?

[@Dutchamp]

I was thinking over to buy Golden lions but as I have seen in your video they arrived with open fillements hmm I still think the parcel has been smashed againsted a wall or something. The had matched them and tested them so it's hard to blame the factory they won't send bad ones. I hear a lot of goods about the sound.

[@faultlessguitarsandamps1116]

Hi Terry . So are the Dynacos a shock hazard without an earth conductor in the mains lead if any wire or component shorted .

[@d-labelectronics]

Hello, nope, they have an internal 3AG fuse. Never had an issue, however I have experienced the terrible hum on units that had been changed to the 3 prong cord. Works fine on guitar amps, but not these Dynacos.

[@jordan390a]

Did that one RCA KT88 show 2.1mA of gas leakage current...? Doesn't that create more tube noise in an audio circuit...???

[@overkillaudioinc]

common issue, resolder the pins. i have seen it dozens of times. bad solder joints

[@kubockferre5532]

hi where can i find a good tube tester .thanks

[@midmodaudio6576]

Excellent video, as all of your videos are. At about 5:24 did you say "rectumfire" ? : )

[@chekizz28]

😁😁😁😁😁

[@cgmasterman]

Where do you get your tubes from🧐

[@patriciakarichko438]

do u repair tube ham equip. for others?

[@d-labelectronics]

Hello, Yes, mostly equipment made in the late 50's

[@jk-mm5to]

Don't be vague. Get Sprague.

[@mikesamra9126]

Terry, the filter can caps that guy put in are not sized right. They look short and even tho they are rated at 500v, you need a 525v cap like the 80/40/30/20 at 550v Authentic cap to be safe. I think the CE Mallory reproductions had some early ones that were mislabeled.

[@d-labelectronics]

Hello, Just double checked, the Filter caps are labeled 525V

[@mfr58]

Not earthing/grounding the chassis is potentially very dangerous. You will be relying on the screened lead from the preamp to carry any fault current if the chassis becomes live. That thin gauge may not be up to the job of carrying enough current to trip the breaker. Also if you have the preamp disconnected and the amps on they will obviously be ungrounded/earthed. Depending on the internal grounding arrangement you could earth/ground the chassis to power ground, and use a safety ground lift circuit to connect to signal ground. Just sayin.

[@pioneerman8467]

Just received a pair from 1961 from my dad looking for some one to pick them up",

[@jp040759]

Wouldn't you want to at least install a polarized 2 prong AC power cord? I see you have Hoppes 9 gun oil on your bench. Is that for SHOOTING trouble?

[@d-labelectronics]

Don't believe it would make a difference, the main transformer primary floats, no connection via noise cap to the chassis.

[@antoniograncino3506]

Gold Lions are Russian make, are they not ? Will you get credit ?

[@roberthickey1465]

I would not deal with that tube supplier again. They could not have possibly matched that quad (if they are the ones doing the matching). I have never seen filaments break during shipping.

[@waynelemieux5111]

SHOW US THE SCHEM. AT THE SAME TIME

[@herbward5240]

Those are the wrong filter caps ! Only the F & T made 600 volt ( surge ) rated caps are the caps to use in the MK III Those CE caps are very marginal in the MK III . Also , a Anatherm inrush current limiter ( perhaps two in series ) is appropriate for the MKIII as that is the 115 volt mains transformer. A high filament supply is not needed.

[@user-zc1xg6sk6g]

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[@pauldow1648]

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