The real situation, nowadays, is that if one wants unused 45's, need to be ready to pay uSs 80+ a piece from the serious people Vacuum Tubes Radio Tubes - 5,000 different tubes in stock - Over 10 million tubes!
Unless you got access to some secret priviliged source...
This winter I'll ask Santa for a quad of Arcturus baloon shaped blueish 45's
Mmm.. cascaded LTP's... it will solve the lack of gain, if one want the amp to be an integrated, feeded directly from the CDP output ...right?
About the filaments, for PP duty, it's better to go AC + hum pot, or regulated DC?
In the Jaime's schema, is it a 45 VDC injection on the filament supply?
Unless you got access to some secret priviliged source...
This winter I'll ask Santa for a quad of Arcturus baloon shaped blueish 45'sMmm.. cascaded LTP's... it will solve the lack of gain, if one want the amp to be an integrated, feeded directly from the CDP output ...right?
About the filaments, for PP duty, it's better to go AC + hum pot, or regulated DC?
In the Jaime's schema, is it a 45 VDC injection on the filament supply?
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That looks like a voltage reading from the drop across the 710 ohm cathode bias resistor.
Cascaded LTP's seem to be perfectly balanced regardless of how mismatched the tubes are. Sometimes a small DC offset adjustment is needed in direct coupled cases. Total gain is about 100 X (voltage) using 6SN7's which is plenty unless feedback is used. Then I use a 6SL7 in the first stage.
Regardless of strong opinions voiced in this forum, Schade style feedback can be applied from the plate of the output tube to the plate of the driver tube in an LTP. Cross coupled Schade can be applied from the output tube plates to the input tube plates to reduce higher order harmonics.
I use a 45 PP. I can say for sure that if one doesn't get at least 5W in class A then the tubes are well used.....
With the right driver they simply sound better than anything around. Maybe a 2A3 PP has more power but the sound is not the same, although very close.
My amp uses a transformer-coupled driver and a simple cathodyne splitter with SE input stage. Tubes are "vintage" 6H30P-DR's for all stages except 45's.
I have made the IT's by myself because they run a little bit different. In few words they don't have the typical limitations of IT's because I use CF on the drivers, through a dedicated winding on my IT's. That's the only sort of FB in my amp and I get more than 6W in class A with THD at 1%.
Nowadays I think it is rather difficult to get a reasonably matched quad of 45's. Especially if they have to be identical. In such case, 80$ each is a very good price!!
I am running a Sylvania quad which I bought as used. They still test very good with 85-90% emission and full gm.
I have two NIB quads, one by RCA and one by Raytheon. The RCA's test as from data-sheet in terms of current-gm values although they appear to be a bit more linear than expected! The Raytheon's are exactly as from data-sheet except they all have approx. 10-15% more gm at any volt-current setting.
45
P.S.
This is my RCA quad:
With the right driver they simply sound better than anything around. Maybe a 2A3 PP has more power but the sound is not the same, although very close.
My amp uses a transformer-coupled driver and a simple cathodyne splitter with SE input stage. Tubes are "vintage" 6H30P-DR's for all stages except 45's.
I have made the IT's by myself because they run a little bit different. In few words they don't have the typical limitations of IT's because I use CF on the drivers, through a dedicated winding on my IT's. That's the only sort of FB in my amp and I get more than 6W in class A with THD at 1%.
Nowadays I think it is rather difficult to get a reasonably matched quad of 45's. Especially if they have to be identical. In such case, 80$ each is a very good price!!
I am running a Sylvania quad which I bought as used. They still test very good with 85-90% emission and full gm.
I have two NIB quads, one by RCA and one by Raytheon. The RCA's test as from data-sheet in terms of current-gm values although they appear to be a bit more linear than expected! The Raytheon's are exactly as from data-sheet except they all have approx. 10-15% more gm at any volt-current setting.
45
P.S.
This is my RCA quad:
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Marcel and Clovis
I heard Marcel and Clovis by Phil Sieg at VSAC two days before 9/11. It was
driving some Audio Classic horns, and I have not heard better. Perhaps some
as good, but none better.
http://www.tubesrit.com/audio/albums/userpics/10001/Marcel_Clovis_DHT_PP45.pdf
Skip
I heard Marcel and Clovis by Phil Sieg at VSAC two days before 9/11. It was
driving some Audio Classic horns, and I have not heard better. Perhaps some
as good, but none better.
http://www.tubesrit.com/audio/albums/userpics/10001/Marcel_Clovis_DHT_PP45.pdf
Skip
45, 46 and 6W6Gt, excellent !!!
I love the 45, 46 and 6W6GT.
When you listen a 45 and listen a 6L6 after, the sound of 6L6 remenber a transistor amplifier !!!
I love the 45, 46 and 6W6GT.
When you listen a 45 and listen a 6L6 after, the sound of 6L6 remenber a transistor amplifier !!!
I've acquired a fair quantity of 45s as well. I did most of it while the prices were on the way up. They fluctuated quite a bit for a while...I think there were a few 45 PP amps being sold on eBay at the time. Most of them have various degrees of wear. I think I have two Raytheon pairs that measure new and match fairly well. I've ended up with around 20 tubes, I think, and a PP 45 amp is something in the back of my mind.
If you have the tubes, you can hardly go wrong. And besides, once you build a great 5w pp 45 amp, (if you need/want the extra power) you can put a pair of 300b in front of them. There's no doubt that 45s sound amazing, but I suspect some of that reputation rests on the fact that they are all single plate and fairly easy to drive with a small signal tube....
Hey All, glad I found this thread. Tomorrow I pick up an old Slivertone radio with 45's in it. I just glanced at a drawing of the tube compliment but I kinda remember it had 8 45's in it. Their were two drivers one looked like a twelve and the other an 8" arranged like the woofers in Linkwitz's latest open baffle design. If the tubes are good I was thinking of a PPP design using fixed bias. RCA datasheet puts P-P output impedance at 3.2K for a pair. That would make it 1.6k. Edcor happens to have a 1.6k transformer at 25 watts for $52 each. Its an ultralinear transformer so I was thinking of using the UL taps for feedback? I was also thinking of 6SL7 driving a 6SN7 LTP. By the way the 45's are Tung Sols.
The thread appears to be quite dated but recently resurrected. I read in the original posts the concern with driving PP 45s, the rather high voltage. Attached is how I did it almost 20 years ago for PP 6AS7/6080s, a very much more difficult requirement.
A simple change allows boot strapping without the UL OPT.
John L Stewart
A simple change allows boot strapping without the UL OPT.
John L Stewart
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I had seen quite a few circuits meant to drive the 6AS7G/6080 family. All looked to be of the 'brute force' variety. Looked like bootstrapping would be a very clean solution to the problem. It is.It is surprising this very obvious circuit would not have been tried sooner. But after I posted it almost 20 years ago no one came back with evidence of its earlier application.
In a later project I tried the 6BQ7 family as replacements for the very expensive 6SL7 & 6SN7. The performance was very impressive, makes one wonder why they are ignored. So I tried them on this one as well, again the results were good. All backed up with careful measurements of IMD & THD.
There were complete articles on both these & several others published in Glass Audio & AudioXpress. I have them with added info in PDFs. Just let me know, I can send them.
Cheers to all, John L Stewart P.Eng
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Hi John,
Would you be so kind as to send me this info? I have a number of 6080/6as7 tubes, as well as a few 6336A tubes that I want to experiment with, and have been looking for suitable ways to drive them in a reasonable way.
I'm trying to cobble something together with things that I have on hand, and was looking at using these tubes because I have them, and also because they seem like they would work with some transformers that I have that are in the 3.4K Ω range.
I need about 20W of clean output from them, so was going to use either two 6080 per channel, or one 6336A
I've done the high voltage thing with 6as7g and 6336a, with the 6as7g my favorite operating point was either 100v across the triode with -33Vg1, but with~200v across the tube with around a -100Vg2 they work well. 6sl7 concertina feeding a 6sn7 LTP works extremely well with around ~320v supply in this case, with room for negative feedback.
I've got a pair of 6336a I'm thinking of digging out and building up soon, I'd love those PDF's too!
I've got a pair of 6336a I'm thinking of digging out and building up soon, I'd love those PDF's too!
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You will have to send me a private message on the forum message service with your email address in order to send the files. They are too large to post here.This might work but could be removed from this message-
johnnhelen4 at gmail dot com
Regards, John Stewart
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