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807 Sound Quality?

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PRR

PRR

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Joined 2003
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> I would like min.10W or 12W from one 1625

Assume SE audio Output will be 33% to maybe 40% of Pdiss.

Work backward. 12 Watts out at 33% efficiency is 36 Watts dissipation. 30W Pdiss at 40% efficiency, but this tends to be higher THD than we like.

You must use multiple 6L6/807/1625. Or a Big Bottle.

> I dont want pay KT88 prices.

Doesn't bother me. Back in the 1970s I was filling big (750 total watts) power amps with big bottles. While the price of a big tube has gone up in dollars, EVERYthing else (almost) has gone up more. I think tubes today are less expensive than ever.

A 6L6/807/1625 will idle at 19 Watts for your whole life. I have pulled factory original tubes out of old amplifiers. Yes, hard-worked guitar amps eat tubes. But PA and hi-fi amps mostly don't.

> 2k HOURS for 90USD

I do not think the KT150 is a good buy for several reasons.

I also suspect good big tubes do more than 2K hours.

However $90/2Khr is $0.045 or 5 cents an hour. Compare this to the cost of ANY other fun you can have. Going to a drinking bar is a couple dollars an hour. Movie theaters are over $5/hour. Watching a 2-hour on-demand movie at home just cost us $6: $3/hour. $0.05/hour is "nothing".

_I_ would pencil a Russian 6550 at $50 and hope for 5,000 hours. That is a penny ($0.01) per hour.

Yes, OK, costs will be different in Brazil because of high import duty on electronics and maybe a strong competitive local beer market (US beer is all over-priced). But not to make the cost of big tubes higher than the cost of other forms of fun.

A decade ago I was working on a SE 6550 for a music school. I fully expected that 6550 (either Sovtek or used vintage TungSol) to last many-many years (long enough for me to leave that place).
 
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kodabmx

kodabmx

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Joined 2011
Miles Prower

Miles Prower

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Joined 2005
dolphin-hsl.com
FullRangeMan said:
Hi,
?I would like lots of info on how is the 807/1625 sound?
Likely will be Russian G807 or the 12V G1625, input stage is 1 tube only 6SN7 or 6SL7, tube rectification, output is one single tube in Tetrode Single Ended A1 about 10W w/low NFB to drive one full range 94dB,8 ohms.
Thanks for help:00
Click to expand...

I would advise against it, as this is likely to sound really bad. Pents, as pents, in SE make a lot more HD than power triodes. There's no getting around that, and you usually saw SE audio finals in cheap equipment and/or where you weren't too concerned with sonic performance.

Secondly, the 807 likes to make h5 and higher order harmonics when used as PP finals. Open loop, this sounds really nasty. You need NFB to clean that mess: I used some 7dbv of lNFB + 13dbv gNFB and got excellent sonic performance from PP 807s.

If you need 10W, you'd do better with PP 6AQ5s or 6V6s if you want the bigger Octal bottles. The 6V6-oids sound better open loop than the 6L6-oids. Such a PP design wouldn't be that much more difficult, and would sound better. It would be a better long term investment.

If you just have to go SE, there are a lot of designs using 300B, 45, 2A3, etc. power triodes. The 812 or 811 running Class A2 SE will do at least 10W. A2 grid drive is NBD if you use source follower grid drivers.

You'll also get better sonic performance as well. The 812 especially is a good audio tube as it was originally intended for use as a plate modulated RF final, and plate modulation is an audio application, and everything that applies to audio sonic performance applies to plate modulators.
 
FullRangeMan

FullRangeMan

Member
Joined 2009
Miles Prower said:
I would advise against it, as this is likely to sound really bad. Pents, as pents, in SE make a lot more HD than power triodes. There's no getting around that, and you usually saw SE audio finals in cheap equipment and/or where you weren't too concerned with sonic performance.

Secondly, the 807 likes to make h5 and higher order harmonics when used as PP finals. Open loop, this sounds really nasty. You need NFB to clean that mess: I used some 7dbv of lNFB + 13dbv gNFB and got excellent sonic performance from PP 807s.

If you need 10W, you'd do better with PP 6AQ5s or 6V6s if you want the bigger Octal bottles. The 6V6-oids sound better open loop than the 6L6-oids. Such a PP design wouldn't be that much more difficult, and would sound better. It would be a better long term investment.

If you just have to go SE, there are a lot of designs using 300B, 45, 2A3, etc. power triodes. The 812 or 811 running Class A2 SE will do at least 10W. A2 grid drive is NBD if you use source follower grid drivers.

You'll also get better sonic performance as well. The 812 especially is a good audio tube as it was originally intended for use as a plate modulated RF final, and plate modulation is an audio application, and everything that applies to audio sonic performance applies to plate modulators.
Click to expand...
I though it was a good idea due the claims of great SQ on the Dennis Had Inspire Sweet 807 stereo amp.
I dont want PP, due heat, tubes price, more parts and wish a SE tone.

811 seems fine to me, I will investigate 812.
Thankyou for help:)
 
Wavebourn

Wavebourn

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Joined 2006
wavebourn.com
Instead of 811 you can use GU-50 connecting all grids together. Great tube, but as cheap as a dirt!

http://www.wavebourn.com/forum/download.php?id=491&f=7

Gubernator_Mk_6b_3.png
 
R

rcollege

Member
Joined 2010
I have done amps that can roll tubes. Very simple Hi Mu drivers to power tube. So far, the 6L6GC's were preferred over EL34's, KT88's, KT77's and 6550's. Triode mode no NFB.

That was until this last amplifier I made.
It uses 1625's driven by 6ER5's. Again triode mode, no NFB.
I kept the voltage high 512V B+, 460V plate to cathode, the current low 26 - 30mA.
13 Watt dissapation at 30mA. Plenty of room to increase current if needed.
I may reduce the cathode to get better harmonics...I believe less IM.

I use hi impedance OPT's - 14K. 41:1 turn ratio... 30mA x 41 = 1.2A, enough current to supply 11 watts with 8ohm speakers...but the trade off is lower voltage to the speaker...so still less power.

Not a ton of power 5.5 watts tops but clear transparent sound. And can fill a small if not decent size room...

Yes this seems unconventional, but it works. Not just to my ears...

I believe and am witness that the 1625 can provide wonderful transparent sound... but it is the circuit as a whole that makes the differences. I have put more time in the pre-amp section and power supply than the power section.


1625...where else can you get NOS military tubes for under $5 per tube? Forget rolling though...not too many 7 pin socket tubes 802 and 837 are the other two...but adjustments need to be made due to lower plate dissipation.
 
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R

rcollege

Member
Joined 2010
Yes, but I would trust the 1625 more as it is more rugged.

It was designed to be used in mobile equipment (12.6V heater) and aircraft transmitters in WWII aircraft. I read that they were used on the B-17's as well as other bombers. Reliability was a priority with these tubes.

The other good / bad thing about the 1625 is there are little to no options for tube rolling...which means you will have to focus on the circuit to get optimum sound rather than putting a different tube in
 
R

rcollege

Member
Joined 2010
In listening to the 1625 amp last night, it seemed a little harsh...I think changing the coupling caps will help. The caps are 33nF and are silver mica...which I have noticed can give an overly detailed edgy sound. Polypropylenes seem to sound much smoother.

I will start a new thread about this amp. I have the pics...just need to draw the schematic.
 
R

rcollege

Member
Joined 2010
djn said:
I bought a Heathkit AA-100 to use all the parts I can to build a PP 807. Don't know if the 807 is a drop in replacement for the 7591. Any guesses?
Click to expand...

I will have to guess "no"

The 807 uses a 5 pin socket - the 7591 uses an octal socket
807 has a top cap for the anode- the 7591 does not
807 has a screen voltage limit of 300V when used in pentode- the 7591 is
440V
807 plate voltage is 600v - 7591 is 550v
807 has a dissipation of 25W - 7591 is 19W
807 heater is 900mA - the 7591 is 800mA ... not big...but it may be big enough if you are heating 4 tubes in parallel.

6BG6 is basically an 807 that uses an octal base... but it doesn't change the other differences.
 
djn

djn

Member
Joined 2004
Thanks Rcollege. When I said I was using the AA-100, I should have been clearer. I built a new chassis and will just use the PXT and OPTs from the AA-100 and other small parts if they can work without hassle. I am only going to build the amp section and PS section.

I have the 807s with top caps and sockets already. I just have to find someone who can weld aluminum without distorting the chassis. Either that or use those rods with a propane torch.
 
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