The Amp Garage

As long as there is no significant change in Plate Voltage, Screen current will change in proportion to Plate current. ...so by lowering the voltage across the screen grid resistor (by 4 V DC as suggested on the schematic) you're lowering the screen current, and this implies (looking at the schemat...

Thanks. Since the discussion extended to the YBA-1A Mk II (the one with the fan), I was perplexed how they say on the schematic to adjust the bias trim pot (R7A) " to allow 4 V DC across the Screen resistor R25 (470 ohm, 10 watt)" I understand how the bias pot adjusts negative voltage for the contro...

Thanks! To the best of my ability, I think the only thing glowing red inside (and it's bright red) are the filaments. There's also a little blue glow nearby but not much. On my YBA-1A schematic - came with the amp - it's a 1972, and the resistor coming off the PT to feed the bias (R33 if I'm correct...

Thanks guys. I will probably get bias pots installed on the YBA-1 amps, for my own convenience but mostly for whoever may get the amps in the future. Reviewing and re-educating myself on the famous 'bias' topic, I noticed how the 70% rule (use 70% or less of current estimated to be present at maximu...

Thanks! Great info!!

no mods on the circuitry (outside of the master volume added on one of them)- power tube screen grid resistors are stock - in this case ceramic, 470 ohm, 10 watt screen resistors in one amp, 1k 12 watt screen resistors in the other. and yes, EL34s with pins 1 and 8 jumpered.

Thanks! The '68 bassmaster is stock except for a master volume mod. I'm the original owner (!) and it came with American made 6CA7s, which lasted over 14 yrs.
The '71 bassmaster is unmodified & likely also had 6CA7s originally.
I'll have to check the schematics & amps.

Hello guys, I have two old 1968-1971 Traynor YBA-1 bassmasters, the ones with fixed bias, but no bias pot. (The big brother, YBA-IIA Mark II, came stock with an adjustable bias pot). Both amps have been competently restored recently, work perfectly. One of the long-time power tubes (EL-34) finally s...

Thanks guys! Just spent a few minutes subbing at V1 to start with- both tubes did make the volume pot more linear than the 12AX7, without any adjustment needed in tone controls. I'm not currently gigging, but using these tubes would probably be very helpful in dialing in the right volume more easily...

Thanks! As you probably know, those 60s-70s Traynor tube amps are pretty rugged both physically and electrically. I did some more reading and research, and the caveat about preamp tube subs for some amps- best I can tell - might be relevant for switching tubes to a higher amplification factor (gain ...

Hello, I have some old bassmaster amps, all 3 preamp tubes are 12AX7. The volume pots on these amps go very quickly from silent (at '0', or say 7 o'clock) to LOUD (at '1', 8 o'clock) to VERY loud at 3 (9 o'clock). Beyond 3, it just thickens up more and starts overdriving. I'm not really interested i...

Hello, I have a two 6l6 power tube Juke amp (small builder in New Hampshire), had NOS tubes for ~ 14 years, but one of them had the pin break & lose vacuum, so replaced with Russian 5881s. The power tube socket nearest the phase inverter tube lights up, but without typical heat and also without any ...

I was wondering about using a simple passive DOD A/B switch to alternate two separate cabs. Head is an old Traynor, they're pretty indestructible, but iirc someone wiser than me said this still may be risky to the output transformer.

We have two lives, and the second begins when we realize we only have one. – Confucius

Hello guys, just a follow-up- the amp started behaving normally (no voltage differences between chassis-ground-neutral sites), likely because in probing things (after unplugging AND discharging capacitors & other standard safety measures), I probably partially fixed a cold solder joint of green grou...