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.
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.
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
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
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.
Eli Duttman said:
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
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
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 Brisindi said:
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. 😀
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 $$$ on a new larger transformer so I hope this transformer would be just enough.. How many ma would 1 6L6 use?
PS: I received your tone circuit schematic via email, thanks.
Thanks,
Sal Brisindi
EDIT:
Eli, You posted your response while I was typing this post. I have smaller transformers I can use for the preamp circuit. I really don't want to spend $$$ 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.
Sal Brisindi said:
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?
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
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
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.
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.
Eli,
Edcor sells a nice power transformer for $60.00 (which I really don't want to spend anymore money than I have to) 800vct@200ma/6.3vac 5amp or a 600vct@200ma/6.3vac@4 amps. Unfortunately it does not a 5 volt tap for a rectifier tube. Attached is the specs for the 800vac transformer.
I was thinking about the phase splitter part of the amp, either using tubes like on your El-Cheapo or a transformer from Edcor like this below.
As this will be the 1st real tube amp I will be building getting ideas from different schematics and not building from 1 particular schematic, your and other opinions is greatly appreciated.
Regards,
Sal Brisindi
PS: What do you mean quad 12 "W" tubes?
Edcor sells a nice power transformer for $60.00 (which I really don't want to spend anymore money than I have to) 800vct@200ma/6.3vac 5amp or a 600vct@200ma/6.3vac@4 amps. Unfortunately it does not a 5 volt tap for a rectifier tube. Attached is the specs for the 800vac transformer.
I was thinking about the phase splitter part of the amp, either using tubes like on your El-Cheapo or a transformer from Edcor like this below.
As this will be the 1st real tube amp I will be building getting ideas from different schematics and not building from 1 particular schematic, your and other opinions is greatly appreciated.
Regards,
Sal Brisindi
PS: What do you mean quad 12 "W" tubes?
Sal,
Phase splitter trafos can be tricky. They can NEVER go inside a NFB loop. I don't see where the Edcor impedance matching trafos will work as phase splitters. The Sowter (England) model 8920 is a good example of a phase splitter trafo.
The XPWR110 power trafo looks interesting. SS rectify and choke I/P filter. A "fudge factor" cap. in front of the 1st inductor will bring the B+ up to 400 VDC. IF that 200 mA. is the RMS current rating for 800 V., Close to 400 mA. of B+ current can be drawn. Exactly what is the 200 mA. rating? Is it the max. DC draw, when a FWCT rectifier is used in combination with a cap. I/P filter? A VA rating of the trafo., as a whole, provides better guidance.
The EL84 and the 6V6 are "12" W. tubes. A group of 4 tubes set up PPP in each channel is what I have in mind, for the Dukane power trafo.
Phase splitter trafos can be tricky. They can NEVER go inside a NFB loop. I don't see where the Edcor impedance matching trafos will work as phase splitters. The Sowter (England) model 8920 is a good example of a phase splitter trafo.
The XPWR110 power trafo looks interesting. SS rectify and choke I/P filter. A "fudge factor" cap. in front of the 1st inductor will bring the B+ up to 400 VDC. IF that 200 mA. is the RMS current rating for 800 V., Close to 400 mA. of B+ current can be drawn. Exactly what is the 200 mA. rating? Is it the max. DC draw, when a FWCT rectifier is used in combination with a cap. I/P filter? A VA rating of the trafo., as a whole, provides better guidance.
The EL84 and the 6V6 are "12" W. tubes. A group of 4 tubes set up PPP in each channel is what I have in mind, for the Dukane power trafo.
Sal,
For what it is worth, I’ve used Edcor WSM 10K/10K and XSM 10K/10K as phase splitters, input as well as interstage, with good results in EL84 and 6V6 P-P amps. I see Edcor has added a variety of new WSM and XSM values.
The smaller WSM iron works great as an input phase splitter, but the core saturates easily so if used as an interstage it should be parallel feed. The larger XSM will take a few maDC on the primary or it can be parallel fed.
I’m not sure what input tube you are using but for interstage phase splitting keep plate resistance below 4K for single-end driver. As an input phase splitter the WSM should work into a 12AX7. The WSM and XSM series are cheap enough to experiment with and compare to various tube phase splitting topologies.
Matt
For what it is worth, I’ve used Edcor WSM 10K/10K and XSM 10K/10K as phase splitters, input as well as interstage, with good results in EL84 and 6V6 P-P amps. I see Edcor has added a variety of new WSM and XSM values.
The smaller WSM iron works great as an input phase splitter, but the core saturates easily so if used as an interstage it should be parallel feed. The larger XSM will take a few maDC on the primary or it can be parallel fed.
I’m not sure what input tube you are using but for interstage phase splitting keep plate resistance below 4K for single-end driver. As an input phase splitter the WSM should work into a 12AX7. The WSM and XSM series are cheap enough to experiment with and compare to various tube phase splitting topologies.
Matt
I though perhaps the DuKane transformer would do the job, but from the drawing I would estimate a secondary resistance 70-100 Ohms - that's good for 200 mA. I'd like to see a bit higher. With choke input, it would be good for close to 300 mA, at about 340V with a solid-state rectifier.
You know what the sad part is, there was a identical Dukane power transformer on ebay this past week I could have bid on. What are the chances that will happen again....
I could have used 2 power transformers with 2 5U4's!
Sal Brisindi
I could have used 2 power transformers with 2 5U4's!
Sal Brisindi
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