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5824 (25B6G) output tube

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I awaiting arrival of some recently-purchased NOS 5824 tubes. The 5824, as I understand it, is a high-reliability version of the 25B6G.

https://frank.pocnet.net/sheets/127/2/25B6G.pdf

It looks like a fun tube, with 7.1 watts output into a 2.5K SE OPT, with only 200 volts on the plate and 135 volts on the screen. Of course, it has a 25 volt heater. With two of them for a stereo SE amp, I could go with series-string heating or standard heating, AC or DC. With 300ma current draw for the heater, I could series string a 12AX7A or similar in an octal base, I guess.

Any thoughts on the best input tube here? It looks like I have to swing a fair amount of voltage to feed this tube, so I'm thinking a high-mu triode but I don't know yet.

And yes, I know I could ditch the whole idea and build a ECL82 amp, but let's pretend that I only want to use this particular tube for this particular build for reasons that make sense to me, even if they don't make sense to you. ;)
 
23 V. peak to peak is not that difficult to get. A CCS loaded 6922 section will easily get there, when fed the 2 VRMS signal from a "standard" CDP. As for a high mu type, consider the 7F7 Loctal that is electrically equivalent to the 6SL7.

A thought, perhaps something along the lines of the 6Y6 amp I worked on with Jeff Yourison might tickle your fancy. Regulate g2 B+ with a 0B2 and go with near Class "B" PP "finals". You can safely exceed the plate voltage max., by a small amount, provided you don't exceed the max. plate dissipation.
 
7W yes, but distorsion 14% !
Perhaps cathode feedback (speaker circuit between cathode and ground) to make thinks a bit better.But then you need 30Vac on the grid.
Something like half of the 12AX7, ECC83 or the russian 6N2P ?
Rk=1k2 , Ra=180k and Vb=200V for an input less then 500mVac,or a bit more if the g1 leak resistor of the 25B6 is small (< 470k).But still room for some overall feedback.
Mona
 
I used a pair of 9GH8s for the input and driver section in my old Parsimon design, which has plenty of excess drive voltage capability. You would need to boost the B+ a bit to achieve your power output target. That could be accomplished by adding a 28~30VAC B+ boost xfmr or by reworking the entire power supply section. Also be aware that my high-frequency tweaks will need attention when a different OPT is used.
 

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I used a pair of 9GH8s for the input and driver section in my old Parsimon design, which has plenty of excess drive voltage capability. You would need to boost the B+ a bit to achieve your power output target. That could be accomplished by adding a 28~30VAC B+ boost xfmr or by reworking the entire power supply section. Also be aware that my high-frequency tweaks will need attention when a different OPT is used.

Nice! I see you are using 70V line transformers as OPTs. How do those sound? I happen to have a bunch of those MCM units myself. Have not used them yet.
 
Parsimon sounds just fine to my ears. No obvious coloration. I spent quite a lot of time dialing in the best performance I could get from those transformers and ended up with amazingly good results even on reactive test loads. Do keep in mind that I'm getting just five watts per channel with the power supply built as documented, which is half of the OPT's power rating. If you try to run transformers like this at rated power and full bandwidth, most of them (all of the cheap ones) will saturate pretty badly at the lowest audio frequencies. They're somewhat equivalent to the OPTs used in old console stereo chassis in that respect.
 
I awaiting arrival of some recently-purchased NOS 5824 tubes. The 5824, as I understand it, is a high-reliability version of the 25B6G.

https://frank.pocnet.net/sheets/127/2/25B6G.pdf

It looks like a fun tube, with 7.1 watts output into a 2.5K SE OPT, with only 200 volts on the plate and 135 volts on the screen. Of course, it has a 25 volt heater. With two of them for a stereo SE amp, I could go with series-string heating or standard heating, AC or DC. With 300ma current draw for the heater, I could series string a 12AX7A or similar in an octal base, I guess.

Any thoughts on the best input tube here? It looks like I have to swing a fair amount of voltage to feed this tube, so I'm thinking a high-mu triode but I don't know yet.

And yes, I know I could ditch the whole idea and build a ECL82 amp, but let's pretend that I only want to use this particular tube for this particular build for reasons that make sense to me, even if they don't make sense to you. ;)

25B6G is a 6Y6G with a 25V heater. Quite a few amps were built with PP 6Y6G in the 50s & 60s. There is one article reproduced in the Audio Antholo
AHsJFJhC1JVdTiwNFHjIzQRYghQooATggIBTTTRlyNVL0Z4COQLoGuCnQgAduFxBEWgoDaMibGzFWSPmU4csj+wM1PKj1okIIUjp6WEESB+BGGKhQHUrj5U6CaosGTVmjgxZfDhtogIpxgAJAgBgmZTpC5kNAxkcmaIq1B1PgSotWCgQzyIagHx4afCnFZqFdF5IKWCKgGENQxAxKdGi1yBCpWrMCCDCAC0TAdrsuGRDyAcYFIJ0QSDAAIIEiQBEYpWEh5JXTySZAQBmxYADD8KQaOQCTi8cXFZ5cGRBDYRUZd6AuiFnIIhOW1QQucCBFxJMLM7QFTgiioNZheYuAgwIADs=
gy series.
 
Thank you all for the information! I truly did not know that the 25B6G is a 25 volt heater version of the 6Y6 tube. Indeed, I like the 6Y6, and in fact have built an amp using the 50C6G, which is a 50 volt heater version of the same tube - didn't know about all these associations, though!

I am thinking to build SE rather than PP, but part of that is my own lack of experience building PP amps. I also tend to go with my traditional schematics that I can understand, as my knowledge is somewhat limited.

I was looking at this one, and I like it:

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Any thoughts?

6Y6s1.gif
 
The 6Y6 is NOT an 25B6 ! With a cathode resistor of 220Ω there is to much current, the tube will overheat.390Ω is more like it (5W is ok).All the rest may stay as is.With this tube the input is less sensitive but not dramatical.
A choke of 15H is perhaps expensive if you find one.More common 10H is good too.
Mona
 
Some Comparisons

The 6Y6 is NOT an 25B6 ! With a cathode resistor of 220Ω there is to much current, the tube will overheat.390Ω is more like it (5W is ok).All the rest may stay as is.With this tube the input is less sensitive but not dramatical.
A choke of 15H is perhaps expensive if you find one.More common 10H is good too.
Mona

Aha!! Someone IS paying attention. So lets have a look at the specs.

Total heater power is the same.
Max plate & screen volts are the same.
But Gm of the 6Y6G & 50C6G is about 40% greater than the 25B6G.
Turns out the 6Y6G is beam while the 25C6G is simply a pentode.
The max output 7.1W vs 6W is accomplished by picking a loadline that gets there.
The 6Y6G & 50C6G will have less distortion at any given power level, a characteristic of beam tubes. Loading would be about the same.
For the 7.1W case we see 15% D. Depending how that was measured, about One Watt.

So aside from biasing, easy to sub into an existing cct either way. A soldering iron & a few minutes will solve that.

The 12/25/35/50L6 family are close enough similar that they too will easily fit into this group.

Beginning in 1957 while I was a poor engineering intern I built several PP 25/35/50L6 amps for friends & enemies. But mostly for money!:)

I will scan some ccts in from my notebook later.
 
A quick look at your proposed cct with Electronic Workbench vers 5 software shows the short path NFB to the 6Y6G cathode would be 7.1 db.

The nfb from the OPT secondary to the 6SL7 cathode would be 12.3 db.

I've assumed the OPT to have 80R primary resistance & the secondary to be 0.5R.

Electronic Workbench has no pentodes. So in the place the 6Y6G is shown as a current source of 7.1 ma/v in parallel with a resistance of 18.3K, both taken from the published data sheet.

Your finished amp will depend a lot on the OPT you choose. Looks very straight forward, should be no glitches at all. The PS is very well filtered.:)
 

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