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What to build?

enzoazul

enzoazul

Well-Known Member
Hello,

I'm planning on building an integrated tube amplifier. Roughly in the 40-50wpc range.

I'd be interested in recommendations as to what circuit to start with... Based on sound quality, simplicity, availability of schematics, parts lists, etc...

Also, am I sacrificing anything building an integrated tube amp, instead of a power amp and a separate preamp? (My original though was to start with a McIntosh 240 or H/K Citation II circuit, but then i'd still need to build a preamp)


Thanks for any thoughts, advice, etc...
 
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Well, I would suggest that the first question to be answered would be how much experience do you have building vacuum tube equipment from scratch?

A vacuum tube integrated amplifier putting out 40-50 watts per channel is going to be a very complex, very expensive project.
 
I'm fairly new to it, but I've built 5 guitar tube amps from scratch. 4 modified Bassman 5F6-A amps and one modified Tweed Deluxe 5E3. They all turned on without issue, and are working fine and sounding great :thmbsp:

I think I could build the tube amp for around $400-$500. Not sure how much the cost would increase by adding integration.
 
Excellent!

In that case, now that we're reasonably comfortable that you aren't going to electrocute yourself, I'll let the more experienced tube guys come up with some circuit suggestions.

Just from my perspective, though, I'd probably be leaning towards a power amp. Much less complex, and you'd be able to use different preamps to get the sound you want.
 
Fisherdude said:
Excellent!

In that case, now that we're reasonably comfortable that you aren't going to electrocute yourself, I'll let the more experienced tube guys come up with some circuit suggestions.

Just from my perspective, though, I'd probably be leaning towards a power amp. Much less complex, and you'd be able to use different preamps to get the sound you want.
Click to expand...

Thanks!

Yeah, I guess the idea of an integrated is rooted in wanting a simplified setup (less pieces of gear) and the attempt to be economical since I don't really have a tube preamp. But there's certainly an elegance to a simple, well designed power amp.
 
If you build enough gain in the power amp, you can get by with a passive pre - keep it really simple an basically make it a stepped attenuator and the right switches to choose among your sources.
 
Buy a Bob Latino ST-120 and get the capacitor upgrade along with the Stepped Attenuator. Excellent!

I still run a passive preamp.... Then for a DAC I run a Decware ZSTAGE. This is nice as my digital music is a mixed bag.. At times 0 gain into the passive pre is good and at times some ZSTAGE boost on the DAC signal is nice.

The ST120 is quite similar to the amp with attenuator battradio just mentioned. a bit higer Watt / channel
 
If you've built guitar amps, then when not start with a basic power amp section using a pair of 6L6GC's. Look at the schematic for a Fender Pro AB763 for example. Take everything from the phase inverter onwards.
 
This one

Fine amp. can use KT88 vs 6550. Fixed bias means no cathode capacitor to color the sound- clean sonics. It is ultra linear, but use 40% taps with this tube family. 6SN7s are known for good performers too. RCA 5Z4G rectifiers are good sounding and a pair is much less expensive than Mullard GZ34 plus puts out more current that is needed for 50 watts.

This UTC 'girl' is begging for it.

Go to Triode Electronics, look at schematics then scroll to 'UTC'. AK will not allow this schematic to be uploaded more than once here or I would have posted it here.
 
Or this one
http://www.audiokarma.org/forums/showthread.php?t=480448

An AK member built it a few months ago and it turned out fine. Not sure you can do it for $500 though. I'm thinking its more like $800.

I would find the absolute simplest circuit possible. They're always harder than they appear. I second goldleaf's comment about passive preamps. It's the only way to go if the amp will have enough gain.
 
Thanks for the suggestions! Lots to look into and research :) Hadn't thought of a stepped attenuator. Like the sound of that
 
Funny you should mention this now.

I'm in progress, of building something very similar.

6L6GC integrated- based on the HK A250 circuit, but converted to fixed bias.

With the right output transformers and operating mode, that can easily top 40 watts. Mine is going to be more like 35 watts, since that's the rating of the output transformers I'm using (from a Scott receiver). But, with something like Edcor 60w outputs, it could do 40-50 watts...

The advantage of the 6L6GC, is that it's got nearly the plate dissipation of the 6550 (30 watts as opposed to 35), it's much easier to drive (requires about 2/3 the bias and signal voltages), and they're EVERYWHERE, and CHEAP.

Though it was a different front end, I did pretty much this exact setup, with my "Mk 6L6" monoblocks. 60 watt Hammond outputs, driven by a Dynaco Mk III driver stage on Mk III chassis. About 450v B+, UL, fixed bias, with 6.6K primary impedance, and about 55ma idle current per tube (could go as high as 60ma, no problem). That same alignment, with the HK A250 circuit, and a single-tube preamp (I'd suggest the 6SN7 or 6CG7, one section per channel), could easily take care of business. If you used a SS rectifier (which I am- and the original HK A250 circuit did), that's only 7 tubes total (one preamp, two drivers, and four outputs). In pentode mode (like the original HK A250 was), it might be closer to 50 watts...

Regards,
Gordon.
 
Last edited:
GordonW said:
Funny you should mention this now.

I'm in progress, of building something very similar.

6L6GC integrated- based on the HK A250 circuit, but converted to fixed bias.

With the right output transformers and operating mode, that can easily top 40 watts. Mine is going to be more like 35 watts, since that's the rating of the output transformers I'm using (from a Scott receiver). But, with something like Edcor 60w outputs, it could do 40-50 watts...

The advantage of the 6L6GC, is that it's got nearly the plate dissipation of the 6550 (30 watts as opposed to 35), it's much easier to drive (requires about 2/3 the bias and signal voltages), and they're EVERYWHERE, and CHEAP.

Though it was a different front end, I did pretty much this exact setup, with my "Mk 6L6" monoblocks. 60 watt Hammond outputs, driven by a Dynaco Mk III driver stage on Mk III chassis. About 450v B+, UL, fixed bias, with 6.6K primary impedance, and about 55ma idle current per tube (could go as high as 60ma, no problem). That same alignment, with the HK A250 circuit, and a single-tube preamp (I'd suggest the 6SN7 or 6CG7, one section per channel), could easily take care of business. If you used a SS rectifier (which I am- and the original HK A250 circuit did), that's only 7 tubes total (one preamp, two drivers, and four outputs). In pentode mode (like the original HK A250 was), it might be closer to 50 watts...

Regards,
Gordon.
Click to expand...


That's very interesting! And more in line with my initial idea. Do you have a thread detailing this current project? Would love any design/schematics info you'd be willing to share.

Thanks!
 
Haven't really gotten to serious assembly on mine yet.

I have not been looking forward to drilling/cutting all the holes in the chassis deck. That's always the biggest PITA for me...

Schematic, is basically the stock Harman HK250 amplifier circuit, just converted to fixed bias, plus my "stupid simple" preamp- which is basically just a 6CG7/6SN7 with about 22K plate resistor, 1.6K cathode resistor, unbypassed, running on about 300v B+... it's really that simple, but it works great. I put the volume control after the preamp tube (between preamp gain and amp), and the source selector before the preamp (naturally :D )...

Regards,
Gordon.
 
In the output-range you're suggesting not a lot of tubes are available today within reasonable cost.
Obviously 6L6 will get you there and so will EL34.
The more interesting, from my point of view, is the 807. With a top-cap yes, but also with the 'looks'; sound/spec's like the 6L6.
Exotic amp-circuits with line-output tubes will also get you there but you'll need to do some experimenting and depend on experience, which you may have or not.
The fixed-bias 6L6, EL34, 807 solution is a no-brainer, more or less, if you stay out of grid-current (AB2). Quality will depend a lot of iron-quality imo. In my country this kind of quality iron alone will cost a good deal more than $500, probably more like $700 including a power-supply choke.
Then there's the rest of the amp... Anyway, a total of $1000 should get you something you don't need to 'upgrade' over and over. In the US maybe 25% less.
Pre-amp on the same chassis with the power-supply and output-amp will gain you some insight in how to avoid ground-loops and how to do real neat wiring. If not you'll head for the waah-room :D
Good luck,

/tri-comp
 
sony6060 said:
Fine amp. can use KT88 vs 6550. Fixed bias means no cathode capacitor to color the sound- clean sonics. It is ultra linear, but use 40% taps with this tube family. 6SN7s are known for good performers too. RCA 5Z4G rectifiers are good sounding and a pair is much less expensive than Mullard GZ34 plus puts out more current that is needed for 50 watts.

This UTC 'girl' is begging for it.

Go to Triode Electronics, look at schematics then scroll to 'UTC'. AK will not allow this schematic to be uploaded more than once here or I would have posted it here.
Click to expand...

BTW-
Like Gordon mentioned keep the audio transformer primary impedance around that 6K ohms impedance. 5K to 6K ohms is higher than tube manufactures recommended impedance. Higher impedance provides a higher dampening factor that makes for an overall more clear & detailed sonic signature- especially so when speaker impedance dips below nominal specs.
 
GordonW said:
I have not been looking forward to drilling/cutting all the holes in the chassis deck. That's always the biggest PITA for me...

Gordon.
Click to expand...

This is how I do it.
...sorry, couldn't resist :D

Best regards,

/tri-comp
 

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GordonW said:
Haven't really gotten to serious assembly on mine yet.

I have not been looking forward to drilling/cutting all the holes in the chassis deck. That's always the biggest PITA for me...

Schematic, is basically the stock Harman HK250 amplifier circuit, just converted to fixed bias, plus my "stupid simple" preamp- which is basically just a 6CG7/6SN7 with about 22K plate resistor, 1.6K cathode resistor, unbypassed, running on about 300v B+... it's really that simple, but it works great. I put the volume control after the preamp tube (between preamp gain and amp), and the source selector before the preamp (naturally :D )...

Regards,
Gordon.
Click to expand...

Nice. Sounds like a good layout. Gonna get to researching. Thanks

Drilling is a PITA. So is hand hammering all the eyelets into the circuit board. But it definitely feels worth it when it's all done, and you know you did it all by hand.
 
tri-comp, sony6060 thanks for the added info and suggestions. Still quite new to tube amps, so it all helps immensely.
 
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