Anyone ever build tube HiFi power amps?

[wcrankshaw]

I'm interested in building a really good reliable tube power amp for a record player set up. Anyone have a suggestion they can point me towards?

[Jazz P Bass]

You could try a search for old Magnavox amps.
Or Fisher.

Any of those & more where good amps.
You will have to watch the RIAA curve on the preamp input.

[wcrankshaw]

thanks - I'll check those out. At the moment I was just planning on using a ready to roll phono preamp. I'm open to suggestions on that, but I've heard phono preamps are really hard to get right.

[Enzo]

Says who?

If you want to listen to records, modern amps and receivers no longer have phono preamps, but they sell stand alone phono preamps in a bunch of places. They work fine.

But for that matter, check any old Pioneer or Marantz or other good brand of stereo receiver, and it will have a perfectly fine phono preamp. ANd the whole thing will sound good to boot. MAny of those even had selectable moving magnet or moving coil selectors for phono cartridge type.

You mention power amp, so aside from phono preamp, do you already have the rest of the preamp? Phone preamp generally means just that, the phono part. All the volume and tone controls and extras like recording outs and monitors and loudness if you want that are in the preamp.

I see from several sources "USB turntables". Audio Technica comes to mind. It is a regular turntable, but it has a digital converter and a USB output so you can record your records into your computer. Burn them onto disc.

Plitron sells a circuit board for a tube power amp.
Tube Amplifier Circuit Board « Plitron

[wcrankshaw]

Enzo, sorry I didn't mean a preamp was hard to get, as in acquire. I meant I've heard that a tube preamp for hifi use is difficult to build successfully with low/no hum, etc. At least as compared to the power amp.

I've got the preamp covered (already have an RIAA preamp, and a different receiver that will also do the job). What I'm trying to achieve is finding sort a gold standard of simple reliable power amps to round out the setup. Something I can hook up a record player preamp to, or an ipod (preamp built in), or whatever.

[Jazz P Bass]

Tube Stereo

Check this out.
I don't know where I got it.
Tube Stereo pdf.

[Steve Conner]

The Dynaco ST70 is an old classic. Clone kits for it are still available from Triode Electronics, for not too much money.

I personally run an old Crown SXA monitor amp that I got as a gutted wreck and restored. It's basically a Williamson design.
scopeblog » Crown Super SXA

There are plenty of designs for tube phono preamps, ranging from the cheap and cheerful to the really exotic. Here are some sensibly priced ones. Phono Preamplifier

They're only "hard to get right" if you want RIAA accuracy to the nearest 0.1dB or whatever, or nothing but parchment-in-truffle-oil capacitors in the signal path. Or if you run a moving-coil cartridge. The tiny output from these is a real challenge to amplify with tubes.

[Rhodesplyr]

Yes, I build tube Hi-Fi power amps, but I was a little puzzled by the direction of this thread, since it seems more focused on phono preamps than power amps, per se.

One thing I'd need to know to advise you is: how much power do you need? My 22wpc Scott 299 does a great job driving fairly efficient speakers in a smaller room, but if you have power-hungry speakers or need to fill a large room, you'd probably want something with more power output.

I'm also not quite clear on whether you just want a stereo power amp or if you want an "integrated amplifier" that has source-switching controls and a volume control built in. Some integrated amplifiers have built-in phono preamps, but some don't.

For a straightforward power amplifier, Roy Mottram's VTA-70 driver circuit upgrade for the ubiquitous Dynaco ST-70 is pretty easy to build and hard to beat for the price and effort required. And you can buy reproduction Dynaco transformers and chassis from a number of aftermarket sources. Used ST-70s used to be a bargain, but most have been bought up since the resurgence of interest in tube audio. Also, to get the best from the output transformers, you really have to install an upgraded power transformer, so, knowing what I know now, I'd probably buy new parts and start from scratch.

DYNAKITPARTS.com

HiFi Home Stereo Amplifier Kits

[wcrankshaw]

Thanks for the links. I'm interested in just the power amp part of the setup with a volume control. I'm not looking for audiophile exactly, just nice tube sound. The reality is that it will be used with things like an ipod or a cheap record player/preamp. the speakers are pretty typical 1980s era big wood paneled boxes. Probably not too incredible on the sensitivity scale. I think they're 60W a piece. It wouldn't be needed to provide enough sound for anything bigger than an average living room. Am I right that 22W per channel would be pretty sufficient for my situation even in lower sensitivity speakers?

[imaradiostar]

I have a Scott 222C that uses a pair of 7189a's per side and it's not the loudest thing in the world but it sounds pretty great. I used to have an amp with two 6l6's per side that was loud as hell- I wouldn't shy away from a design like that for casual stereo listening. I would probably want just a little more wattage for large inefficient speakers.

I think if I had to make something like that today I'd use a pair of largish 50 watt outputs (leftover from the 6l6 stereo amp), a quad of modern El34's and a Fender twin reverb power transformer. I'd probably end up with a triode/pentode tube as the gain stage and phase inverter for each side, with negative feedback injected at the cathode of the pentode and the triode as the phase splitter. It would be simple and straightforward. You could do something similar with 12dw7's and they'd probably be easier to keep linear.

jamie