Germino Lead 55 Trouble - We Summon The Amp Gods:

The ECC82 in the V3 really brought out a warm fullness to the amp and noticeably less white noise.

How do you think ECC82 will fare in the 3rd spot from a longevity standpoint???
 
Robert Herndon said:
I put the old Russian El34 tubes in that had 464VDC and the amp sounded fuller and cleaner, if that makes any sense????
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Robert Herndon said:
I can't figure out how to measure the bias, let alone change it.

My DSL40C'S have 2 pots. This has only one.

How do i work with only one bias pot???

Where do i measure Mv???
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This is when you have to let go of the OCD. Most amps only have 1 bias pot. You already have your plate voltage of 464 volts, so you will want to set the bias for 33-39ish ma depending on how hot you want to go. I would shoot for 36 and recheck the plate voltage. I use a VHT bias meter, so not exactly sure which pins you need to probe and does the amp have 1 ohm resistors on the power tube groungs?
 
The green wires to the preamp tubes are the grid wires that lead to the grids of those tubes. The grid wires to V1 are very sensitive, especially if they are not shielded. The popping that you hear when touching those wires or its corresponding resistor and/or socket pin is quite normal.
 
syscokid said:
Those are 2 or 3 watt carbon comp voltage dropping resistors. Both are grey-red-red-silver banded: 8.2k with 10% tolerance each.
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20200301_121541.jpg
I just started populating my JMP50 board yesterday, so this is a rather convenient opportunity to see what the pros are doing. I'm finding schematics with 2 8.2k, 2 10k or one of each. No consistency it seems. Thanks for your resistor marking knowledge!
 
Cadorman said:
View attachment 39331
I just started populating my JMP50 board yesterday, so this is a rather convenient opportunity to see what the pros are doing. I'm finding schematics with 2 8.2k, 2 10k or one of each. No consistency it seems. Thanks for your resistor marking knowledge!
Click to expand...
So there's 3 possible combinations with those resistor values: 16.4k... 18.2k... and 20k. It depends on much voltage you want to drop from the main B+ voltage to the PI circuit. At least it will be easy to swap out those resistors and tune to your liking. You may or may not notice a difference.
 
Cadorman said:
This is when you have to let go of the OCD. Most amps only have 1 bias pot. You already have your plate voltage of 464 volts, so you will want to set the bias for 33-39ish ma depending on how hot you want to go. I would shoot for 36 and recheck the plate voltage. I use a VHT bias meter, so not exactly sure which pins you need to probe and does the amp have 1 ohm resistors on the power tube groungs?
Click to expand...

Ya, i am not sure how to bias this one...
 
Hi Robert, sorry I haven't been here at this thread of late. Here is a full instructional on how to bias the power tubes
This is for an amp with a duet, or pair of power tubes. Make sure you have a fully charged battery/batteries in your multimeter & the amps impedance selector is switched to the correct impedance setting for the cab you hook to it.
Many people simply bias the tubes to 70% of maximum plate dissipation & this is fine, though the 'scope method of "fine tuning the bias" (least amount of crossover notch distortion) shown in the Lee Jackson video that plexi67 linked will sound best (the amp does need to be biased in a suitable range before attempting this).
To accomplish the same result without a 'scope, I bias to 60% & note (write down) the negative bias voltage. I then bias to 70% & again note the negative bias voltage..
I then play through the amp at volume to find where it sounds best between these two bias settings. Hope this helps. Cheers
 
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