RH807 with a pentode driver?
- Thread starter dnewma04
- Start date
Hey now
wasn't trying to say they were expensive. Just not pennies on the dollar. My thought was, once you got off the beaten track (loctal, something you don't see in many {common} builds), I would assume the would be cheaper. 25 ain't a bad thing at all. What I noticed more was they look scarce. Stock up.
This all interest me because I've been looking for a wierd(off the b track) tube for use in a PP 8K load set up. I had looked at loctal, and well thats as far as I got. Just very early dream stage still. Have 2 -3 in front.
wasn't trying to say they were expensive. Just not pennies on the dollar. My thought was, once you got off the beaten track (loctal, something you don't see in many {common} builds), I would assume the would be cheaper. 25 ain't a bad thing at all. What I noticed more was they look scarce. Stock up.This all interest me because I've been looking for a wierd(off the b track) tube for use in a PP 8K load set up. I had looked at loctal, and well thats as far as I got. Just very early dream stage still. Have 2 -3 in front.
dnewma04
The Healer
Hey now
This all interest me because I've been looking for a wierd(off the b track) tube for use in a PP 8K load set up. I had looked at loctal, and well thats as far as I got. Just very early dream stage still. Have 2 -3 in front.
With an 8k PP OPT, I'd think some 7C5s would be a good choice. Or, you could do something silly like C3g in push pull.
25.00 is pretty reasonable considering these tubes once sold for a few hundred dollars each.
dnewma04
The Healer
I love distractions.
Scuzzer
Fixed Bias
Hey Jay, thanks for the boards. Old Mrs. Nguyen from up the street dropped them by late tonight even though you addressed them correctly. Nothing like having an 70 year old Vietnamese woman trying to describe how she ended up with circuit boards.
Our local postal service representative is spot on as always...
Our local postal service representative is spot on as always...
6au6 / 807
Hi,
Sorry to wake up an old post but I'm presently having some difficulty with a pentode driven SE 807. I'm using the 6AU6 as a driver and it's not working too well, my output power is down the drain and I wonder why ? Would someone care to share their design ?
TIA
Isophon
Hi,
Sorry to wake up an old post but I'm presently having some difficulty with a pentode driven SE 807. I'm using the 6AU6 as a driver and it's not working too well, my output power is down the drain and I wonder why ? Would someone care to share their design ?
TIA
Isophon
Attachments
Kegger
R.I.P. 1/12/1966 - 6/1/2017
With using the pentode driver as a pentode, you'll get a lot more feedback as apposed
to the original triode, I would suggest upping the size of your feedback resistor, try at
270k verse that 150k, and see how it looks, if still not enough gain try 470k and so on.
to the original triode, I would suggest upping the size of your feedback resistor, try at
270k verse that 150k, and see how it looks, if still not enough gain try 470k and so on.
Dude, if you did that on my bench, you could build an Eico HF81. I've had the OPTs and a power transformer that would work (from a Motorola tube TV) laying on my bench for a year or more, just waiting for (taunting?) me...
Regards,
Gordon.
With an 8k PP OPT, I'd think some 7C5s would be a good choice. Or, you could do something silly like C3g in push pull.
25.00 is pretty reasonable considering these tubes once sold for a few hundred dollars each.
I built a Magnavox AMP175/8802 clone with PP 7C5s, and a pair of 8K OPTs from an old 6GW8 amp (Knight, IIRC). Came out wonderfully. Eleven of the best-sounding watts I've personally heard, per channel. Dave Gillespie and some of our other local friends measured it at less than .14% distortion at full power... waveforms looked great, and it sounded great.
I used 12AX7s for the input tubes... if I had it to do again, I'd use 7F7s. A little less gain, but if you went with 470K plate resistors on the input stage (instead of 220K, that I used- that's easy to tune in), you could get at least some of that back...
Regards,
Gordon.
PakProtector
AK member
hey Dave,
I think I could convince Paul to relinquish the C3m I loaned him. Then you could try w/o laying out cash and if you liked them then get your own later.
cheers,
Douglas
mashaffer
Super Member
dnewma04
The Healer
Douglas, thanks for the offer. I ended up buying a quad of C3gs off ebay shortly after I started the thread for a price a good 25% under typical prices.
If I might comment, I would like to point out that if we are talking about the Schade style feedback - the above quoted imho is NOT CORRECT.
Actually, the first tube should be automatic bias with an unbypassed resistor (the driver tube). Therefore, no LEDs or similar...
The output tube should be used as a tetrode/pentode, not in ultralinear mode...
To avoid being misunderstood, the circuit would certainly WORK, but most of the obtainable "improvements" would be lost by turning off some of the "improving technology" feedback.
BTW: when I first designed an RH amp (the RH84) internet was still dial-up in Serbia -- besides not having had the chance to see the RCA manual implementation of anode-anode feedback (on PP amps), at that point I had never heard of Schade.
I am still not much knowledgeable when it comes to this engineer, all I know is that he did some important work during the '30s. But, what I read on Schade and RCA manual implementation, the feedback is different than the 1st generation of RH amps particularly in the precision or "aggressiveness" of the application (i.e. much higher Rfb values, they did not have spice at the time and of course they had their own toughts about what they were doing).
I therefore ask, why is there so much insisting on calling the anode-to-anode feedback "Schade style" - why not "Alex Kitic style" or "RH amp style"? What has he done for you that I have not?
Kegger
R.I.P. 1/12/1966 - 6/1/2017
Alex, first off Schade style feedback has been used by many on many designs.
(and for a very long time, even before we were born)
Look at Petes KT88 SE amp, All of Dougs Push Pull amps, various vintage amps
including some very old RCA amps, was Pioneered by Schade so we call it that.
(it's nothing against you using it, but we've called it Schade and used it a lot)
--------------
Second my implementation of Using the UL tap I want/need less feedback, and
that is why I use LED's in the way I use them for biasing the driver, if running a
output tube in pentode I would not use the LED to get the more feedback, and
or running the series resistor between that drivers plate and feedback resistors.
(there are various ways to run this type of feedback scheme)
It's all about implementation that best suits what yur running, not 1 size fits all.
(I prefer the UL implementation over pentode mode, and is why I run this driver)
(and for a very long time, even before we were born)
Look at Petes KT88 SE amp, All of Dougs Push Pull amps, various vintage amps
including some very old RCA amps, was Pioneered by Schade so we call it that.
(it's nothing against you using it, but we've called it Schade and used it a lot)
--------------
Second my implementation of Using the UL tap I want/need less feedback, and
that is why I use LED's in the way I use them for biasing the driver, if running a
output tube in pentode I would not use the LED to get the more feedback, and
or running the series resistor between that drivers plate and feedback resistors.
(there are various ways to run this type of feedback scheme)
It's all about implementation that best suits what yur running, not 1 size fits all.
(I prefer the UL implementation over pentode mode, and is why I run this driver)