Need assistance with picking the right Edcor audio transformer

[Sal Brisindi]

Hi All,
I am gathering parts to build a PP 6L6 stereo integrated amplifier with bass/treble controls and I can use your expertise/opinion.

I will only be using 8 ohm speakers so the 4/8/16 ohm transformer is not necessary unless I would use the 16 ohm tap for negative feedback. I did purchase a set of transformers from Triode a while back but I think they would be to small for this amp.

I have a nice NOS Dukane power transformer with a bias tap for this amp. Which audio transformer should I purchase? I would think either the 4,200 ohms or the 6,600 ohm transformer. You can go to Edcorusa.com for additional info on the transformers.

Thanks,
Sal Brisindi



Here is a mock-up of my amp with the Triode transformers. I have since purchased a 12"x10"x2" black Hammond chassis so I won't be using the chassis shown in the photo, come to think of it, I think I will need a larger chassis with the larger transformers. The relay sockets are only used to hold up the 6L6 tubes. I would probably only use 3 12AX7's instead of 4 but that is another matter. I will also turn the power transformer 90 degrees.

[Eli Duttman]

Sal,

6.6 KOhms end to end for 6L6s. A single O/P tap sounds better. So, the Edcor model you want is CXPP60-8-6.6K, which costs approx. $60 each.

I'll EMail you some tone control circuitry.

Wimpy 'X7s are a poor choice directly in front of 6L6s. Use a Mullard circuit with a 12AT7 in the splitter/driver "hole".



edit: added topology suggestion

[jon_010101]

What voltage do you plan to run? I just got a pair of their 6k6 transformers for a 6BG6GA (6L6GC with plate cap) amp -- I'll be running 400-450V.

[Sal Brisindi]

Originally posted by Eli Duttman
Sal,

6.6 KOhms end to end for 6L6s. A single O/P tap sounds better. So, the Edcor model you want is CXPP60-8-6.6K, which costs approx. $60 each.

I'll EMail you some tone control circuitry.

Wimpy 'X7s are a poor choice directly in front of 6L6s. Use a Mullard circuit with a 12AT7 in the splitter/driver "hole".



edit: added topology suggestion

Hi Eli,
Thanks for your input. I have plenty of 12AT7's, 5751's, 12AU7's, 12AX7's, 12BH7's I can use. I think you emailed me some tone circuits a few months back. I have to check my laptop.

Don't worry, your El-Cheapo will get built before my 6L6 amp.. ;-)

I am just at the gathering parts stages...

Jon,
I will post the specs of my power transformer later tonight. I happen to have a nice quad of 6BG6 tubes also.....

Regards,
Sal

[Sal Brisindi]

Jon,
Here is a link to the spec sheet of my Dukane power transformer. It is in PDF format. Looks like it will produce 400VDC @ 200ma

That should be enough for a stereo 6L6 PP integrated amp.

http://www.tuberadios.com/temp/dukane.pdf

Regards,
Sal Brisindi

[Eli Duttman]

Originally posted by Sal Brisindi
Jon,
Here is a link to the spec sheet of my Dukane power transformer. It is in PDF format. Looks like it will produce 400VDC @ 200ma

That should be enough for a stereo 6L6 PP integrated amp.

http://www.tuberadios.com/temp/dukane.pdf

Regards,
Sal Brisindi

Sal,

Just me, I like to see 2X the DC draw as the AC RMS rating of the rectifier winding, for a cap. I/P filter PSU. If I'm reading the specs. correctly, your trafo's rectifier winding comes up short. FWIW, I'd rectify with a 5AR4 into a 22 muF. 1st filter cap., which eases the pressure on the rectifier winding, starts slowly, and gives a few extra Volts to drop in the DCR of the filter choke too. I'd also use that trafo to power only the 4 6L6 "finals".

It's no secret that I like PSUs with big cujones. The B+ PSU in "El Cheapo" can (sic) easily deliver 200 mA.

[Sal Brisindi]

Looking at the Dynaco ST-70 power transformer specs, the B+ can handle 300ma, where as my transformer can handle 200ma, might be to small for my application, any opinions on this?

Thanks,
Sal Brisindi

EDIT:
Eli, You posted your response while I was typing this post. I have smaller transformers I can use for the preamp circuit. I really don't want to spend $$$ on a new larger transformer so I hope this transformer would be just enough.. How many ma would 1 6L6 use?

PS: I received your tone circuit schematic via email, thanks.

[jon_010101]

Originally posted by Sal Brisindi
...I have smaller transformers I can use for the preamp circuit. I really don't want to spend $$$ on a new larger transformer so I hope this transformer would be just enough.. How many ma would 1 6L6 use?

Hello Sal,

You will probably want to draw 50-60mA per tube at idle at ~450V. If you used another transformer for heaters, you might be "okay", but right at the limit for idle -- really not a great place to be

So, I'm guessing you don't have a second Dukane transformer?

[Sal Brisindi]

Jon,
I don't have another Dukane power transformer. This is a set back for my 6L6 tube amp, I might have to scrap the idea....

I have other power transformers with specs on them but they are under rated for this application and other transformers without specs. I can always measure the output voltage but I will not know the current ratings..

Thanks,
Sal

[Eli Duttman]

Sal,

Look here for some "typical" 6LCGC operating conditions. Links to complete data sheets are provided too.

Don't give up on that Dukane power trafo. If you SS rectify and choke I/P filter the B+, enough current will be available to feed a PP amp that uses a quad of "12" W. tubes in each channel. O/P trafos usually associated with EL34s would be used. Yes, the "El Cheapo" splitter/driver will do just fine. The 5 V. winding would be used (via voltage multiplication) to feed the B- rail.