Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: uki on April 29, 2022, 12:40:32 pm

Title: help identify which tubes
Post by: uki on April 29, 2022, 12:40:32 pm: Hey guys !!

Which PA tubes could be used in the following circuit(may be wrong)?

The B+ I'm guessing something around 420v rectified by 5y3(gt maybe), PT 350-0-350.

Thanks in advance !
Title: Re: help identify which tubes
Post by: kagliostro on April 29, 2022, 01:10:15 pm: Pinout corresponds with 6L6 tubes but also EL34

Voltage is compatible with both tubes if I remember well

Franco
Title: Re: help identify which tubes
Post by: uki on April 29, 2022, 06:31:16 pm: Thanks Franco, that is what I was thinking, much appreciated !
Title: Re: help identify which tubes
Post by: tubeswell on April 30, 2022, 10:11:07 am: Quote from: uki on April 29, 2022, 12:40:32 pm
B+ I'm guessing something around 420v rectified by 5y3(gt maybe), PT 350-0-350.

5Y3 won’t supply enough forward current to make a pair of 6L6s sound good. Cathode-biased 6V6s will sound happy.

A 5AR4 will work in the same 5V 2A winding and will work good with a pair of 6L6s, provided that the High Tension winding can deliver at least around 180mA (preferably 200mA)
Title: Re: help identify which tubes
Post by: uki on May 01, 2022, 08:29:55 am: Quote from: tubeswell on April 30, 2022, 10:11:07 am
Quote from: uki on April 29, 2022, 12:40:32 pm
B+ I'm guessing something around 420v rectified by 5y3(gt maybe), PT 350-0-350.

5Y3 won’t supply enough forward current to make a pair of 6L6s sound good. Cathode-biased 6V6s will sound happy.

A 5AR4 will work in the same 5V 2A winding and will work good with a pair of 6L6s, provided that the High Tension winding can deliver at least around 180mA (preferably 200mA)

The PT
pri 115v 50cy
sec 350-0-350 200mA
5v 4A
6.3v 5A CT
Title: Re: help identify which tubes
Post by: luthierwnc on May 01, 2022, 11:07:43 am: I would have guessed EL34 because of the 1k screen resistor. And yes, a 5Y3 won't get it done. When in doubt, I always look at the Duncan power supply calculator: http://www.duncanamps.com/psud2/ sh
Title: Re: help identify which tubes
Post by: HotBluePlates on May 01, 2022, 01:40:39 pm: Quote from: luthierwnc on May 01, 2022, 11:07:43 am
I would have guessed EL34 because of the 1k screen resistor. ...

"1kΩ screen resistor" doesn't really mean anything. Any tube could potentially have that value screen resistor.

That there is no indication Pin 1 (EL34 Suppressor) is tied to Pin 8 (EL34 cathode) is a strong indication it is not an EL34. That link is mandatory, except when the suppressor is tied to a negative voltage.