The 807 is the same as a 6L6 in a RF cloathing, nothing else. Since the 6L6 was designed as an Audio output tube the 807 should work just as well.
Any circuit that is good for a 6L6 should work fine with an 807. Remember though that as a single ended output amplifier there is a considerable amount of DC current in the output transformer. To work well there has to be an Airgap in the iron of the output transformer. That adds cost because the transformer has to have a lot more iron and copper for a reduced output power. The 6G6 should work fine as a driver for the 807. But to design a driver seems to be a lost art. People seem to just copy an existing design without really understanding what they are doing and why.
I happen to be a professional circuit designer, and I am supposed to know what I am talking about. Hans J Weedon.
Any circuit that is good for a 6L6 should work fine with an 807. Remember though that as a single ended output amplifier there is a considerable amount of DC current in the output transformer. To work well there has to be an Airgap in the iron of the output transformer. That adds cost because the transformer has to have a lot more iron and copper for a reduced output power. The 6G6 should work fine as a driver for the 807. But to design a driver seems to be a lost art. People seem to just copy an existing design without really understanding what they are doing and why.
I happen to be a professional circuit designer, and I am supposed to know what I am talking about. Hans J Weedon.
By the way: Since the load impedance of a loudspeaker varies all over the place an 8Ω speaker as stamped on it may have a minimum impedance of
4Ω and a maximum of 25Ω at resonances. So in my opinion any load impedance within a factor of two of optimum should be more than good enough.
It is only when you test the amplifier on the bench with a resistive load that it matters which load impedance is optimum. As far as I am concerned if it sounds OK it is good enough. Instead og using an 807 try a 6BG6 it is the same tube but with an Octal socket instead of the old multipin socket.
Hans J Weedon. PS: to find if a tube is the same as look and compare the heater power. You will find that any power tube with 6.3V at 0.9A is a 6L6 variant. At least that is what I have used as a guide.
Hans J Weedon
4Ω and a maximum of 25Ω at resonances. So in my opinion any load impedance within a factor of two of optimum should be more than good enough.
It is only when you test the amplifier on the bench with a resistive load that it matters which load impedance is optimum. As far as I am concerned if it sounds OK it is good enough. Instead og using an 807 try a 6BG6 it is the same tube but with an Octal socket instead of the old multipin socket.
Hans J Weedon. PS: to find if a tube is the same as look and compare the heater power. You will find that any power tube with 6.3V at 0.9A is a 6L6 variant. At least that is what I have used as a guide.
Hans J Weedon
Thank for your answer!
I don't think I can use my power of transformer at 300V it is already 325VAC.
I must pick some tube for a higher voltage, two candidate KT88 or 300B
Originally I collected this transformers for a SE 300B but I having second thoughts if I can build that.
(as a first tube project) I built many many solid state but not a tube amp from scratch.
My power transformer has only one 0-325V, a SINGLE tap and most of tube power supply schematics they use a center tapped transformer or 2 x ### VAC.
To bad in case if I can use it because it is a beefy 5.5Kg potted transformer.
If I am unable to use that transformer I think I give up my tube amp dreams.
I would like to use SS bridge, a non tube rectifier.
Can someone confirm if I can use this power transformer for a stereo amp? Thank you.
I have a pair 3.5K transendar for outputs and a 200mA 6H potted choke a dozen 6SN7 and some D3a tubes for inputs but NO power tubes.
Attachments
I don't think you have to worry about your power transformer with 325V AC it gives a lot of voltage out, I know, but a design using a 6L6 veriety
power amplifier can use anything up to 550V the tube really do not care as long as you don't exceed the power dissipation of the anode. A 6L6 can stand a dull red anode for about 3 minutes while you readjust the current dow. Tubes are not like transistors that take seconds to plow if you exceed any of the parameters, especially over voltage. For instance the 6BG6 (a 6L6 lookalike) can easily take 6kV on the anode for a short time. by a short time i mean 10µs. A 5.5lb power transformer into a 1kV solid state bridge rectifier should give you a good 450V DC out. 450V is high for a 6L6 amplifier, look in the RCA tube handbook, I think you will find power amplifiers with that voltage on the final output. They got a 100W out of a pair of 6L6s or 807/6BG6 if you will. Now!!. 550V is a lethal voltage and you must work with one hand in your pocket because you will die from a shock at that voltage level. Between 300 and 600V is the lethal voltage range. Fortunately you only die once in life, but it can be contagious..
Hans Jørgen Weedon.
power amplifier can use anything up to 550V the tube really do not care as long as you don't exceed the power dissipation of the anode. A 6L6 can stand a dull red anode for about 3 minutes while you readjust the current dow. Tubes are not like transistors that take seconds to plow if you exceed any of the parameters, especially over voltage. For instance the 6BG6 (a 6L6 lookalike) can easily take 6kV on the anode for a short time. by a short time i mean 10µs. A 5.5lb power transformer into a 1kV solid state bridge rectifier should give you a good 450V DC out. 450V is high for a 6L6 amplifier, look in the RCA tube handbook, I think you will find power amplifiers with that voltage on the final output. They got a 100W out of a pair of 6L6s or 807/6BG6 if you will. Now!!. 550V is a lethal voltage and you must work with one hand in your pocket because you will die from a shock at that voltage level. Between 300 and 600V is the lethal voltage range. Fortunately you only die once in life, but it can be contagious..
Hans Jørgen Weedon.
You can certainly use that 325v ac transformer . Take a diode bridge followed by a swinging choke (not a singer). In case you haven't heard of that, a swinging choke means that after the rectifier first comes the choke and then the smoothing capacitor. Usually it's c-l-c now it's l-c. The result is a dc voltage that is 0,9 times the transformer voltage in your case about 300v dc. at 1,4 times the original current (although that's not an issue here). Usually it's followed by another choke plus capacitor. If you want to know more about swinging chokes check wikipedia.
Lets design a 285VDC B+ using your 0-325VAC secondary:
Your 0-325V Secondary can be used with a Solid State Bridge Rectifier, and a choke input filter.
If the choke has "critical" inductance.
A very approximate example for critical inductance, if the power mains are 60Hz, and the bridge rectifier is full wave (120Hz).
Suppose the DC load is 50mA, the approximate critical inductance is 350 / 50 = 7 Henry.
If you use a 10 Henry 100mA choke you should be good, with margin to spare.
In your case, with 325VAC secondary, a solid state bridge, and a choke, you can get up to about 292VDC minus the voltage drop in the bridge and the choke (choke DCR x Load current).
Suppose the choke DCR is 100 Ohms. 100 Ohms x 50mA = 5V drop in the choke DCR.
Including a 2V drop in the bridge, you will get about 285V DC.
If you need a little more B+ than 285VDC, put a small capacitance in front of the choke, it can raise the B+ voltage.
Will that work for you?
One more thing to consider, what is the current rating of the 0-325VAC secondary?
For 50Hz full wave rectification, change the formula from 350 / load mA = critical inductance; to 420 / mA = critical inductance
(and as always increase the Henry a little, to have some margin).
Your 0-325V Secondary can be used with a Solid State Bridge Rectifier, and a choke input filter.
If the choke has "critical" inductance.
A very approximate example for critical inductance, if the power mains are 60Hz, and the bridge rectifier is full wave (120Hz).
Suppose the DC load is 50mA, the approximate critical inductance is 350 / 50 = 7 Henry.
If you use a 10 Henry 100mA choke you should be good, with margin to spare.
In your case, with 325VAC secondary, a solid state bridge, and a choke, you can get up to about 292VDC minus the voltage drop in the bridge and the choke (choke DCR x Load current).
Suppose the choke DCR is 100 Ohms. 100 Ohms x 50mA = 5V drop in the choke DCR.
Including a 2V drop in the bridge, you will get about 285V DC.
If you need a little more B+ than 285VDC, put a small capacitance in front of the choke, it can raise the B+ voltage.
Will that work for you?
One more thing to consider, what is the current rating of the 0-325VAC secondary?
For 50Hz full wave rectification, change the formula from 350 / load mA = critical inductance; to 420 / mA = critical inductance
(and as always increase the Henry a little, to have some margin).
If you take a look at the first picture I posted all the information from the power transformer available is there. It is on the transformer.
It is a 0.25A DC.
The choke I have; Classification Rect. , Filter choke, 200mA, 6 Henry, 85 Ohms.
To be honest I worry about if we make it to work I only get a couple Watts before the higher level distortion kicks in.
I had a Philips SE tube amp with some modification, it sounded OK with Jazz but when I was listen to a classical it was almost a torture.
Sometimes the sound was too low with my Visaton DIY speaker, other times (when it got loud) it become too distorted.
For Jazz at low level in a small room was acceptable.
My speakers about 87db + room gain.
Because of that I sold the amp (still miss it),I made a promise to myself if ever I buy or build something it must have at least 6-7 Watts power.
I worry if I go with low(er) V power supply I end up another amp what I can not enjoy with all type of music.
I am not for disco or boom boom.
Just normal level + if I need to increase the volume still have some (1-2 Watts) clear power.
6L6GC tube also a promising type with 3.5K output transformer. Price is much better than the KT.
Maybe I will have to replace, swap the output transformers with 4.7, 5K for 807 tubes.
I like that tube, I like the shape of the glass. Coke bottle shape.
Or I invest in a pair 300B or KT88 and keep the OPT.
A bit pricey for experimenting, what can I do?
Thank you for all for ALL OF YOU for the reply..
If you use a solid state rectifier with a choke input filter, add a 0.1 uF capacitor (1.6 or 2KV!) or a 500-600V MOV from plus to minus before the choke - otherwise the rectifier will short sooner or later from switching transients. 3.5K will work with the lower supply voltage.
Hammond marketed a line of swinging chokes while PP Class B Audio amps were common.
All gone the way of the Dodo now, but something might be available on the used market.
This ad from 1960.
Attachments
Looking at the specs on the power transformer you'll see that it has multiple primaries. Wall voltage is typically a bit over 120v in most areas. If you run 120+V from the wall into the 110v primary you'll have more than 325v on the secondary. The heater winding will also be higher, of course, but you can use dropping resistors to get it in line.
I wouldn't worry about using a 3.5k OT. Tubes are quite flexible when it comes to load. And, as someone already pointed out, the actual load from a speaker will vary at different frequencies, depending on its impedance curve, so the primary impedance of the OT fluctuates during actual use.
You should have enough clean power using the 807 or 6BG6, no need to spend a lot of money on other tube types. Unless you use an alternative tube that produces at least 2x the power, you won't notice the difference.
It takes 2x the power (a 100% increase) to create a 3db increase in sound. That's the equivalent of moving 39" closer to your speakers. So, if your amp is producing only 50% as much power as an alternative tube, a 3db increase is possible if you go from 50% to 100%. But that's only if you listen to the amp at full volume.
If your amp produces 75% as much power as one using an alternative tube, the difference between them is a 33% increase. So that will result in a whopping 1db of additional volume but, again, that's only if you listen to the amp at full volume.
At normal listening levels you'd only get a tiny fraction of a db more. Probably the equivalent of tilting your head forward while listening at your normal level. So, in the real world, the power difference (if there actually is any) will be unnoticeable.
I made some more research about the mentioned tubes. I think I will chose the Russian 6L6GC equivalent, the coin base, military type.
Reason; Even if it cost a bit more those tube life time about 5000 hours VS the 1000 type. Octal tube socket, compatible with EL34, KT88
The output transformer 3.5K the best choice. I can find more schematics with this tube which help with my build. I am not set up with scope just basic DMM's. I also read the 6L6GC is a sweet sounding tubes many people prefer that over the EL34 which sound "darker". The octal tube socket allows me to test other tubes like KT's. To start I will order 4PC of the mentioned Russian tubes about 100 bucks with shipping. For the input also I would love to use the octal base 6SN7G tube. I will do more search on that as soon as I order the power tubes. Thanks for the help! think this is the best compromise for me.
Reason; Even if it cost a bit more those tube life time about 5000 hours VS the 1000 type. Octal tube socket, compatible with EL34, KT88
The output transformer 3.5K the best choice. I can find more schematics with this tube which help with my build. I am not set up with scope just basic DMM's. I also read the 6L6GC is a sweet sounding tubes many people prefer that over the EL34 which sound "darker". The octal tube socket allows me to test other tubes like KT's. To start I will order 4PC of the mentioned Russian tubes about 100 bucks with shipping. For the input also I would love to use the octal base 6SN7G tube. I will do more search on that as soon as I order the power tubes. Thanks for the help! think this is the best compromise for me.
Found the App. Plug in tube type from the list supported, SE or PP, B+, Etc.
The App lists the power out, Bias required & so on. Very good & saves a lot of time.
https://www.vtadiy.com/loadline-calculators/power-stage-calculator/
Many years ago I got 4 sovtec 6L6gc 's (a friend bought them at New Sensor). When I tried them I thought something was wrong with my amp as it sounded veiled all of a sudden. Putting in my old RCA 6l6's it sounded open again. This was more than 20 yrs ago so maybe a later stock sounds better.
It's possible that the sovtecs would sound better after a while but I never tried that.
I'm curious whether other forum members have a similar or different experience with these tubes.
Today I had some time and I made some measurements on the power transformer.
The transformer (AC) the Neg has two connections without major change on the voltage of the 6.3V heater.
Pin 1 and 2.
If I use pin 1 and pin 5 (120V) It gives 340V no load. If I use pin 2 and pin 5 it give 364V no load.
If I use pin 2 and pin 3 (marked 100V) it gives max. 430V no load but that increase the heater voltage also to 8V.
At least I know I have those options and I know the transformer works because never tested since I purchased from Canuck Audio Mart.
I found out that G-811 tube also can be used under certain circumstances. Yes, I found some interesting schematics.
Unfortunatelyall Russian (Soviet) tube only can be ordered from Ukraine or Moldova but not from Russia thorough Epay. Price wise not the best time to order tubes now.
Just found out today.
The Russian 6L6GC ; The type they told sound great it has the coin base. I think that is not produced by Sovtecs made by Reflector.
The JJ Tesla 6L6GC sound very nice to (so the EL34, KT88) I heard (compared) against the Electro Harmonix type on YouTube.
Price wise not too bad the JJ either.
The transformer (AC) the Neg has two connections without major change on the voltage of the 6.3V heater.
Pin 1 and 2.
If I use pin 1 and pin 5 (120V) It gives 340V no load. If I use pin 2 and pin 5 it give 364V no load.
If I use pin 2 and pin 3 (marked 100V) it gives max. 430V no load but that increase the heater voltage also to 8V.
At least I know I have those options and I know the transformer works because never tested since I purchased from Canuck Audio Mart.
I found out that G-811 tube also can be used under certain circumstances. Yes, I found some interesting schematics.
Unfortunately
all Russian (Soviet) tube only can be ordered from Ukraine or Moldova but not from Russia thorough Epay. Price wise not the best time to order tubes now. Just found out today.
The Russian 6L6GC ; The type they told sound great it has the coin base. I think that is not produced by Sovtecs made by Reflector.
The JJ Tesla 6L6GC sound very nice to (so the EL34, KT88) I heard (compared) against the Electro Harmonix type on YouTube.
Price wise not too bad the JJ either.
Attachments
From those numbers, your wall-voltage may be 125. (Mine is, most days.) Putting 125V into a nominal 100V winding is likely to smoke the transformer "eventually" (not right away). Pins 2 and 6 seem to be 125V nominal and good for today's voltages. If you plan to use this for many decades you may want to try to make the 1+6 (130V) connection work. We may be there in the year 2055.
Yes, the coin base versions are the ones you want. There is no problem ordering tubes from Ukraine or Moldova. The tubes are the same regardless of where the seller is located.Unfortunately
I have recently ordered tubes from Ukraine and not had an issue, just check the seller's feedback as you would normally do. Unless recent feedback indicates a problem, I wouldn't worry. If the tubes don't arrive you won't have any problems getting a refund. Ebay and Paypal do an excellent job of protecting buyers.
He hasn't posted the schematic he's planning on using after deciding to use 6L6GCs rather than the 807s. It's entirely possible that the 364v option is sufficient.
But if he does need the maximum voltage available, is it safe to assume that the potential for damage would be foretold by the heat generated when the transformer is wired that way?
I've been using an industrial control transformer wired in similar fashion for many years. It is, however, rated for 500mA whereas the one shown here is only 250mA. The one I'm using barely gets warm even after running all day. And I do mean barely, I've actually wondered if it might be running too cool. The amp is a Class A PP 6B4G and the power supply draws ~263mA which includes current drawn by bleeder resistors.
It also has no heater windings. Separate filament transformers are used to heat all the tubes. If his PT runs on the warm side using a separate filament transformer might be one way to reduce the stress on it and, at the same time, provide the correct heater voltages.