Not used to hifi but designed and built >10 guitar amps.
I’ve got a quad of matched 807’s. Is planning a stereo amp build for my jazz and classical (also some metal) loving son for vinyl playing.
Was initially thinking of a regular pp amp but since I had a quad I was thinking stereo. Been searching the net and found the heathkit series and Stancor.
Do want to take advantage of the coke bottle style so want to skip the 6SN7 and run 6F8G’s (two 6J5’s in one bottle) instead Then I realized that I had 10 pieces of JAN 7193 tubes (one 6J5 but top capped grid and plate). Would look way cooler with eight 7193 up front and the heater current draw is 0.3A (half of a 6F8G).
Regarding the 807’s I was thinking a Vp of 400-450V.
So my questions are:
1) a stupid idea?
2) triode or UL operations? Do not need +70W output
3) have this PT from an old PA amp, will it be sufficient? I can always add an extra filament transformer. Will this PT work?
4) the PT does not have a 5V winding and read that an indirected rectifier tube (like a 5v4 or gz37 if preferred). Any way of getting a 5V output from one of the windings?
5) What are the optimal OPT’s for such a stereo amp. With regards to wattage. Frequency response I was thinking 20Hz-20kHz. Could get a custom made toroidal OPT with or without a UL tap for fairly cheap. I do have one 40W 6.6K:8Ohm as
of now with hifi specs. Is stereo really needed?
6) a choke and what would the “optimal” inductance be? Due to the rectifier choice?
7) any drawbacks with using two 7193’s instead of one 6F8G?
If anyone has a similar schematic for a PP hifi amp it would be very much appreciated.
I’ll attach the schematic from where I could get the PT from.
I’ve got a quad of matched 807’s. Is planning a stereo amp build for my jazz and classical (also some metal) loving son for vinyl playing.
Was initially thinking of a regular pp amp but since I had a quad I was thinking stereo. Been searching the net and found the heathkit series and Stancor.
Do want to take advantage of the coke bottle style so want to skip the 6SN7 and run 6F8G’s (two 6J5’s in one bottle) instead Then I realized that I had 10 pieces of JAN 7193 tubes (one 6J5 but top capped grid and plate). Would look way cooler with eight 7193 up front and the heater current draw is 0.3A (half of a 6F8G).
Regarding the 807’s I was thinking a Vp of 400-450V.
So my questions are:
1) a stupid idea?
2) triode or UL operations? Do not need +70W output
3) have this PT from an old PA amp, will it be sufficient? I can always add an extra filament transformer. Will this PT work?
4) the PT does not have a 5V winding and read that an indirected rectifier tube (like a 5v4 or gz37 if preferred). Any way of getting a 5V output from one of the windings?
5) What are the optimal OPT’s for such a stereo amp. With regards to wattage. Frequency response I was thinking 20Hz-20kHz. Could get a custom made toroidal OPT with or without a UL tap for fairly cheap. I do have one 40W 6.6K:8Ohm as
of now with hifi specs. Is stereo really needed?
6) a choke and what would the “optimal” inductance be? Due to the rectifier choice?
7) any drawbacks with using two 7193’s instead of one 6F8G?
If anyone has a similar schematic for a PP hifi amp it would be very much appreciated.
I’ll attach the schematic from where I could get the PT from.
How much power are you looking for? The big challenge is going to be an output transformer that will tolerate the feedback you're likely to employ.
If you can live with 25wpc, I would suggest a Williamson (I always suggest a Williamson!). Your preamp tubes are perfect for this type of circuit, and 807's will run fine with up to 400 volts on the screen, either in triode or ultralinear mode.
Heyboer of Michigan makes a very fine copy of the Peerless S-265-Q output transformer, which you can use with one of the Heathkit Williamson designs, like the W2. This is what I do and I can send you a schematic for improving stability. There are also some higher-powered amps in this article, page 166, using the Peerless:
https://www.americanradiohistory.com/Archive-Electronics/50s/Electronics-1955-04.pdf
I don't know if they will ship overseas, but I'd be willing to forward you a pair if the shipping isn't outrageous. ;-)
There's a Williamson build here using an Edcor transformer:
https://audiokarma.org/forums/index.php?threads/williamson-ultralinear-amp-w-edcor-opt.1011032/
The key of course will be the output transformer and the compensation networks to create a stable amp. I don't know what transformers you're able to access in Sweden. Lundahl? Sowter? (They make a traditional "Williamson" output transformer.) A toroid would work. Anything from 6.6K to 10K plate-to-plate will work for a Williamson, but it needs to have very good bandwidth or it won't tolerate the feedback. Do you have a scope and testing equipment? My suggestions above are known quantities that can be built with confidence. Past that you are on your own. 🙂
Regarding the power transformer, if it's only for a single channel it will likely not power a stereo amp. You would need something with more current capacity. A toroid would work well in this scenario and be pretty affordable.
Anyway, those are some ideas, I hope it helps. 😎
If you can live with 25wpc, I would suggest a Williamson (I always suggest a Williamson!). Your preamp tubes are perfect for this type of circuit, and 807's will run fine with up to 400 volts on the screen, either in triode or ultralinear mode.
Heyboer of Michigan makes a very fine copy of the Peerless S-265-Q output transformer, which you can use with one of the Heathkit Williamson designs, like the W2. This is what I do and I can send you a schematic for improving stability. There are also some higher-powered amps in this article, page 166, using the Peerless:
https://www.americanradiohistory.com/Archive-Electronics/50s/Electronics-1955-04.pdf
I don't know if they will ship overseas, but I'd be willing to forward you a pair if the shipping isn't outrageous. ;-)
There's a Williamson build here using an Edcor transformer:
https://audiokarma.org/forums/index.php?threads/williamson-ultralinear-amp-w-edcor-opt.1011032/
The key of course will be the output transformer and the compensation networks to create a stable amp. I don't know what transformers you're able to access in Sweden. Lundahl? Sowter? (They make a traditional "Williamson" output transformer.) A toroid would work. Anything from 6.6K to 10K plate-to-plate will work for a Williamson, but it needs to have very good bandwidth or it won't tolerate the feedback. Do you have a scope and testing equipment? My suggestions above are known quantities that can be built with confidence. Past that you are on your own. 🙂
Regarding the power transformer, if it's only for a single channel it will likely not power a stereo amp. You would need something with more current capacity. A toroid would work well in this scenario and be pretty affordable.
Anyway, those are some ideas, I hope it helps. 😎
Thank you for your comprehensive reply. I’d took the bait. Since I stumbled in from the guitar world there are some things I don’t get, or just a lack the basic knowledge. - 25wpc?
I do have a scope and a signal generator that I just used for troubleshooting before. Not to calculate harmonics. Will have to learn that.
If you would care to share your improved schematic for the heathkit Williamson it would really be beneficial.
And once again, thank you for your help/inputs and for taking your time to help me with my project. I think the boy would be very happy and I would really like to see those tubes together 🙂. Probably a true joy for the sight. If a stereo amp eight 7193’s, four 807’s and a rectifier. A lot of mass and unfortunately the electricity is really expensive now due to the Russian attack on Ukraine.
- So you don’t think my 40W, 6.6K primary 20Hz-20kHz toroidal OT will work?
- a waist to build in mono or should I dig out another stronger PT and buy another OT with the same specs to build a stereo amp while I’m already in the build process?
- about the choke. Should I max the highest possible Henry according to the rectifier tube?
- one dude said that SS rectification is the way to go for tube hifi when others are highly endorsing tube rectification. Just a matter of taste?
I do have a scope and a signal generator that I just used for troubleshooting before. Not to calculate harmonics. Will have to learn that.
If you would care to share your improved schematic for the heathkit Williamson it would really be beneficial.
And once again, thank you for your help/inputs and for taking your time to help me with my project. I think the boy would be very happy and I would really like to see those tubes together 🙂. Probably a true joy for the sight. If a stereo amp eight 7193’s, four 807’s and a rectifier. A lot of mass and unfortunately the electricity is really expensive now due to the Russian attack on Ukraine.
Yes, your toroidal output transformer will work, in fact it's fine for a 20-40 watt amplifier. If you know the brand and model you should order one that's the same.
You can build a stereo amp, it's just very heavy. ;-) I prefer monoblocks, but stereo is fine. If a stereo amp, I would use solid-state rectifiers, otherwise you will probably need two tube rectifiers, which gets clumsy and expensive. The type of rectifier is sometimes for sonic preference, but more often a consideration of the other power supply components and the amount of current you need to supply.
For a choke in a typical PP amplifier, you only need 5-10 henries. Some people even dispense with the choke, since common-mode noise is cancelled at the output, but I think a choke offers slightly better regulation and reduces ripple noise considerably.
As for bandwidth, a decent PP amplifier should provide at least 20-20K. The original 1947 Williamson amplifier offered 20Hz to 200kHz! Unfortunately it tended to be very unstable and would oscillate into any sort of capacitive load. A revision was offered that included a step filter at the input, reducing the upper bandwidth to around 100kHz, but it still left a lot to be desired. For a good primer on the first American Williamson and it's issues and cures, read here:
https://audiokarma.org/forums/index.php?threads/regilding-the-gilded-lily-heaths-w-2m.767851/
That thread also gives you a good idea of how to use a scope to look for instability. The author of that thread also tested the Heyboer copy of the Peerless S-265-Q and pronounced it very good. He gave me some tips for my own build. The schematic is below. It is very stable and VERY musical.
For this amplifier in stereo, you could substitute a 350-0-350 toroidal power transformer and solid state diodes to replace the tube rectifier. Something like this:
https://www.antekinc.com/as-3t350-300va-350v-tube-transformer/
You can build a stereo amp, it's just very heavy. ;-) I prefer monoblocks, but stereo is fine. If a stereo amp, I would use solid-state rectifiers, otherwise you will probably need two tube rectifiers, which gets clumsy and expensive. The type of rectifier is sometimes for sonic preference, but more often a consideration of the other power supply components and the amount of current you need to supply.
For a choke in a typical PP amplifier, you only need 5-10 henries. Some people even dispense with the choke, since common-mode noise is cancelled at the output, but I think a choke offers slightly better regulation and reduces ripple noise considerably.
As for bandwidth, a decent PP amplifier should provide at least 20-20K. The original 1947 Williamson amplifier offered 20Hz to 200kHz! Unfortunately it tended to be very unstable and would oscillate into any sort of capacitive load. A revision was offered that included a step filter at the input, reducing the upper bandwidth to around 100kHz, but it still left a lot to be desired. For a good primer on the first American Williamson and it's issues and cures, read here:
https://audiokarma.org/forums/index.php?threads/regilding-the-gilded-lily-heaths-w-2m.767851/
That thread also gives you a good idea of how to use a scope to look for instability. The author of that thread also tested the Heyboer copy of the Peerless S-265-Q and pronounced it very good. He gave me some tips for my own build. The schematic is below. It is very stable and VERY musical.
For this amplifier in stereo, you could substitute a 350-0-350 toroidal power transformer and solid state diodes to replace the tube rectifier. Something like this:
https://www.antekinc.com/as-3t350-300va-350v-tube-transformer/
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As mentioned by @hooman above I think the G2 voltage limitation is going to complicate the Ultralinear solution. You might need a design with a lower B+ or triode wired (in which case the G2 rating is increased) or pentode with regulated screens. I use a type of 807 (5B/254M) in my Quad IIs and they work fine there, so maybe you get away with it, but it can be the situation where the 807's can vary amongst the brands how they handle the G2 voltage.
The 807 is fine with 400VDC on the screen. It was used that way in thousands of early American Williamson amplifiers without issues. In fact it's not unusual to find DIY Williamson amps from the 1950's with their 807's still performing well. The data sheet itself allows a max of 400VDC plate/screen voltage in triode mode. You DO need to watch the dissipation, which is 25 watts. When I use 807's or 5933's in my Williamsons, I run them with about 420 volts on the plate and 36-38 volts cathode bias, for c. 380 volts from plate/screen to cathode and 23 watts dissipation. As long as you stay below 400VDC across the tube and under 25 watts dissipation in triode or UL mode, they're fine.
Thanks. I’m leaning towards pentode mode with regulated screens. Maybe by adding two vr150 and one vr105 to be certain that the G2 will be below 405V. Also a fun solution 🙂. I really don’t think the amp is going to be run that hard. A lot of wattage for a home hifi use.
Your life will be much simpler of you use the 807s in triode. No feedback loop. Just 2 stages - 6SN7 or equivalent into the 807s. You can use either a long tailed pair for the input stage or a normal voltage stage with a concertina after it. The concertina (cathodyne) doesn't even have to be a tube - it can be a mosfet. Or you could use an interstage phase splitter like the Lundahl LL1660/10mA. I always find 2 amplification stages are cleaner than 3 so I always plan for that in my amps.
I have a load of 7913s but abandoned all of them for the CV1135 aka CV6, which sounds much better, cleaner, smoother and more detailed. Be warned that the top caps on this are the other way around from the 7193. Good as the CV1135 is, and it's very good, I don't use it because I don't like exposed top caps - you have around 150V on the anode and that's in the top cap which some fool might pull off and play with. So I'd use your 6F8G - safer. You'd have a good sounding amp and a much simpler build.
I have a load of 7913s but abandoned all of them for the CV1135 aka CV6, which sounds much better, cleaner, smoother and more detailed. Be warned that the top caps on this are the other way around from the 7193. Good as the CV1135 is, and it's very good, I don't use it because I don't like exposed top caps - you have around 150V on the anode and that's in the top cap which some fool might pull off and play with. So I'd use your 6F8G - safer. You'd have a good sounding amp and a much simpler build.
If you lean that way you could consider this one: https://audiokarma.org/forums/index.php?threads/the-1625-amp-mk-ii.778418/ Circuit schematic added below.
Note the EFB(tm) circuit to modulate the bias as well as screen voltage, the benefits of which are well documented. Search on “Dave Gillespie EFB”
Your 6F8Gs could be used in place of 6CG7. I’m. ot sure about maximum voltage on 7193, but they are also similar.
@andyjevans, interesting to hear you prefer CV1135 over 7193. Unfortunately CV1135’s require $$$ now.
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@andyjevans, interesting to hear you prefer CV1135 over 7193. Unfortunately CV1135’s require $$$ now.>>
Yes, definitely prefer CV1135, it's a lovely valve. I have a few of them - PM me if you are interested. No silly prices.
Yes, definitely prefer CV1135, it's a lovely valve. I have a few of them - PM me if you are interested. No silly prices.
For building amp with 807 tubes You should look at STC 807 Application Note and 807 RCA 39 page datasheet + STC 807 43 page datsheet.
You can find them here :
https://frank.pocnet.net/
You can find them here :
https://frank.pocnet.net/
I know that my life would be much easier if it’s triode strapped but then the problem arises with my OT’s. 6.6K:8Ohm and a pair of triode strapped 807’s would probably like 3K load. Could use 4 ohm speakers I guess but wouldn’t it be a waste of OT capacity since they are rated for 40W each? A triode strapped PP 807 amp puts out about 15W/channel.
As I wrote previously I’m new to Hifi and just wants the best possible sound out of my tube lineup that I have at home. 807’s and 7193’s. They also look cool🙂.
- Will a triode strapped amp sound “better” than a well regulated pentode version?
- doesn’t only two stages require a preamp os some sort? I would like to keep it all in one chassis.
- no FETs in this amp but an transformer PI would absolutely be an option if it adds anything. The Hammond series if interstage transformers aren’t that expensive.
The only transistor that will be added to this amp is a possible Bluetooth receiver.
Then the speaker decision… have my basement filled with nice alnico speakers from the 50’s but more suited for guitar I guess. Tough call.
6,6k plate to plate is fine for a pair of triode wired 807s. If you want power, you can always push the grids into the positive region.
Was planning on a cathode biased amp. But 15W/channel might be enough. Have to sleep on it. The VR tubes would have been a nice addition to the appearance of the whole thing with their nice glow and shift in intensity with the difference in screen voltage. All the decisions….
807 is the Volvo 240 of tubes: Works for everything, not particulary good at anything... 😎
Oh, I don't know about that. When I use them in my Williamsons they sound lovely. Given that it's hard to find a new power tube for less than $50 nowadays, NOS 807s or 1625s
for around $10 each look pretty good.
for around $10 each look pretty good.
It was a bit of a joke. 807 makes nice triodes but they are somewhat limited by their screen grid voltage rating and low output power. Some datasheets says 400V in triode connection and the low output power can be overcome by A(B)2 operation. I have ha pair of PP monoblocks with triode wired 807s, producing 13W in class A2 @ 295V and 5,6k. I'm currently working on a another pair of SE monos, squeezing 3,5W out of a single 807 @ 360V and 8k plate load.