Hello everyone, starting a new project. I picked up a pair of lowery organ amps. From 1958 holiday ls models. Going to run as mono blocks. Power tube are 6v6gt pp. But the power supply ran 20+ tubes in the organ. So was wondering if the PS. Would support tubes with higher output? Maybe el34s?
Thanks for your Input.
Thanks for your Input.
Might have to be parallel 6v6s. You might not have enough voltage to really use el34s. You likely have the heater and plate power. Anyway, have a schematic of the original units?
Schematic shows 320 volts on the 6v6gt plates, not sure what that voltage would work with, other than the 6v6gt's?
The yy part of the transformer is labeled 12.6V 8A which would mean it was meant to power a whole lot of tubes like 12ax7, 12au7 or so. The xx 6.3 volts 5a is more than enough for the 6v6s and 6sn7 which come out to 1.6A. Some of the extra current rating on the xx likely ran some tubes that used a 6.3 volt heater.
Do you plan to use the output transformers or replace them?
The 340v plate voltage might be a little low to make good use of EL34s.
Parallel 6v6s look easy. You have the heater supply and plate current for it.
You may be able to run a quad of 6L6s as a guess. You would just need to run the heaters in series on the 12 volt yy.
Do you plan to use the output transformers or replace them?
The 340v plate voltage might be a little low to make good use of EL34s.
Parallel 6v6s look easy. You have the heater supply and plate current for it.
You may be able to run a quad of 6L6s as a guess. You would just need to run the heaters in series on the 12 volt yy.
Notice the -20 volt bias comes from the 120 ohm 10W resistor. Most of the current pull for that may come from the 20+ small signal tubes. Bias circuit would need some rework.
I plan on purchasing new/other OPT's. I'll match them to my speakers. Which are home made planar magnetic all neodymium magnet units. With almost perfectly flat impedance at 6.5 ohms. But more power would be better.
And I plan on adjusting everything to match the speakers. Speakers are everything. Amps are just a trial. Not sure 10 watts will push them, but I know 20 will.
I guess next question is if there is a place for an extra pair of power tubes that is close to the original pair. Are there external power sockets that could be knocked out?
You may be able to get 360 volts on the plate supply if you get rid of the 120 ohm resistor in the center of the plate supply.
A quad of 6v6s may get you close to 20 watts UL. You can get a little more with 6l6s or 5881s. The power transformer should get you 25 watts if you pick the right output transformers.
You may be able to get 360 volts on the plate supply if you get rid of the 120 ohm resistor in the center of the plate supply.
A quad of 6v6s may get you close to 20 watts UL. You can get a little more with 6l6s or 5881s. The power transformer should get you 25 watts if you pick the right output transformers.
What about solid state rectifier, wouldn't that bump the plate voltage as well. Not ideal though.
Another question, and I'm sorry for so many, I'm really new to the tube approach. If I went with UL output transformers, the 315v tap on the DC wouldn't be needed? So less pull on the B+?
Tube rectifier is dropping about 25 volts. I guess the big question is how much power are you looking for? It would be great if we knew the power transformer current rating. I would say it was at least about to do 175MA but it could do more.
If you measure the power transformer HV primary voltage you can avoid some guessing.
If you measure the power transformer HV primary voltage you can avoid some guessing.
It depends on what you want to use for output tubes. A pair of 6v6s will not get you past 10W UL.
You might get 20 W with a quad of 6v6s.
You might want to study the tube datasheets for 6v6, 6l6, 5881. Tung Sol 5881 datasheet has a good example for UL configuration if you look.
If you move up to 6l6s or 5881 you can tolerate more plate voltage and get more power either with a pair or quad. There is enough heater current with the transformer to support more tubes.
You might get 20 W with a quad of 6v6s.
You might want to study the tube datasheets for 6v6, 6l6, 5881. Tung Sol 5881 datasheet has a good example for UL configuration if you look.
If you move up to 6l6s or 5881 you can tolerate more plate voltage and get more power either with a pair or quad. There is enough heater current with the transformer to support more tubes.
Another note is in the stock unit you are dropping 20v in the bias resistor from the HV CT and ground. The rectifier drops about 25 volts.
Stock amp shows 340 volts on the first cap which goes to the output transformer CT. They show 20 volts dropped in the output transformer which is typical.
With UL configuration the screen voltage is the same as the plate. You usually can have slightly higher screen voltages in UL compared to pentode as far as ratings go.
You are mostly worried about screen power dissipation in most cases. Worst case screen dissipation happens when the plate voltage swings to zero. In the case of UL with 50% taps, the screen would be at half voltage if the plate swings to zero. Worst case screen dissipation is avoided.
Stock amp shows 340 volts on the first cap which goes to the output transformer CT. They show 20 volts dropped in the output transformer which is typical.
With UL configuration the screen voltage is the same as the plate. You usually can have slightly higher screen voltages in UL compared to pentode as far as ratings go.
You are mostly worried about screen power dissipation in most cases. Worst case screen dissipation happens when the plate voltage swings to zero. In the case of UL with 50% taps, the screen would be at half voltage if the plate swings to zero. Worst case screen dissipation is avoided.
Pretty sure it's 310v. Have to jumper out the power plug for the external tubes. But seems weird, I would think across the whole coil it would read 620v, not 2.5v, either side to center tap, 310v ? Maybe I'm just confused?