Tube Amp Archive

omg..... I recently switched to a ground bus. I made sure that the chassis would only connect at one single point to ground. Therefore I also switched to isolated speaker jacks.... In other words, the OT secondary was not grounded at all...... Just forgot the wire. The older amp has is, but in black...

Hi Everybody, just got my latest 6L6 amp up and running. I do build in a switch for global negative feedback in my amps. Now surprise: with gnf I get a bad hum. I measured 200 Hz (my power line is 50 Hz). Only that frequenzy, no 50 or 100 Hz. I made sure it´s not positive feedback by exchanging the ...

Hi, I checked all wires again, no resistance between the orange and the others (tested with a Fluke 179). 235 VAC is not balanced, 300mV on one side, 235VAC on the other. Now surprise: I figured out that fuse did not burn after switching on the amp and then touching the orange wire to the ground bus...

Hi everybody, just putting a new amp together, with a Classic Tone 18096 power transformer. (Vibrolux Style). The fuse burns, when I switch it on. I norrowed it down to the orange wire. If I do not ground it, everything seems fine. I did use this transformer before and I did ground the orange wire. ...

Thank you for your help! Yes, changing the phase of one primary helped in both cases. The TubeTown PT actually had a piece of paper in the box explaining the correct wiring, I could not find any info whatssoever for the TubeAmpDoctor PT. Measuring with a 12 AC source worked very well. With the wrong...

Hi Everybody, I got an EL84 amp working. It currently uses a ClassicTone 18056 power transformer. Since this is not available no longer, I bought two replacement power transformers for sound testing. One is the TAD MJTM18WP and the other one is a TubeTown tt-ma18pw. Surprise: with both of these PTs ...

Hi everybody, tried out some "cold clippers". I found several on the last stage before the cathode follower (in front of the tone stack) in several famous amps. So it is simply an unbypassed cathode resistor. The Marshall JCM 800 has 10k, Cornford MK50HII 15k, Soldano SLO 100 and Meas Dual Rectifier...

Thank you guys!
@pdf64
perfect answer (with great documentation)
I just figured out that I downloaded this file already in 2014....

Hi Everybody, I put a booster tube (12ax7) "in front of" a JMP-Style amp. So just an extra tube (only one side used of course) before the original V1. Works fine and sounds good (better turn the master volume down...) :-) I checked with my USB oscilloscope and got some "strange" findings though. I a...

Thank you all so very much! In my amp the issue was obviously the multiple chassis to ground bus connections. Actually, isolating the speaker jacks from the chassis did not make any difference. Also the jacks for the effects loop (which was not populated yet, except the jacks were grounded to the gr...

Hi Everybody! First thank you so very much for your help! I use this power transformer: https://www.tubeampdoctor.com/en/mains-transf.-for-marshall-jtm45-and-50w-plexi-tad-kit-plexi-45 It´s a Marshall remake. It does have a filament center tap and I use it. Actually I measured 6.305 Volt, so PERFECT...

Hi Everybody, just finished a new amp project. This time an EL34 amp. I did build quite a few 6L6 amps. The new one has basically the same layout, just different transformers and power tubes. The hum level though is a lot higher. Basically I have a JMP and a Blackface (without Reverb) channel, the l...

yes, the real ´64 Blackface Fender Vibroverb with a JBL D130F installed
it has an issue, but it is not an reissue

Hi everybody, did turn on my ´64 Vibroverb the first time in a year or so. If I play the guitar very lightly, it works fine, if I do a loud single note or a chord, the amp get´s extremely loud (louder than it should be at volume set between 2 and 3 it feels) and it sounds very broken, like fuzzy, fa...

Thank you Martin,
I used the TAD Biasmaster and all four new tubes (JJ KT77) are very close.