Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: nateflanigan on March 22, 2015, 07:49:42 am
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I know this topic has been broached a few times,but I thought I'd start a thread to document/ask for help with what will hopefully be a cool project. The IT guys at work found out I build guitar amps, they'd really like me to build them a tube stereo system. This is new to me, but seems like fun. These guys aren't audiophiles, so I'm not going to have to face all the caps north, or use unobtanium wire or some such nonsense. The features requested are, turntable input, and a line input.
I'm thinking of using this for the phono input
http://www.hagtech.com/pdf/cornet2.pdf (http://www.hagtech.com/pdf/cornet2.pdf)
And this for a line stage
http://www.hagtech.com/pdf/clarinet.pdf (http://www.hagtech.com/pdf/clarinet.pdf)
And possibly this for the power amp
http://diyaudioprojects.com/Tubes/EL84-Mini-Block-Amps/ (http://diyaudioprojects.com/Tubes/EL84-Mini-Block-Amps/)
It doesn't seem like it should be hard to adjust either power supply to accommodate all of the gain blocks. Does anyone see any red flags? Or a path of least resistance?
Those HiFi guys do some wacky things with the heaters.
Any input or advice would be greatly appreciated.
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Look like that power amp project is self-split push pull rather than having a proper phase inverter. I suggest you copy an old Dynaco or Mullard EL84 design. (Or one of those designs with modern improvements.)
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Funny you mention that, I was just looking at the Dynaco st-70. I'll check out the mullard stuff too. Thanks
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The IT guys at work
give 'em an input for their I-stuff and an A/D out and they'll love you forever!
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The Dynaco ST-70 is a great amp in terms of performance/$ ratio, but if you wanted to go a little smaller/ cheaper the Dynaco ST-35 is also good. Seems like with modern tube audiophiles the temptation to 'reinvent the wheel' or "guild the lilly" is big... but those engineers back in the day knew a thing or two about getting the best sound and specs for a reasonable price.
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Having been in the home entertainment business my entire working life I would say that my first tube amp project, a Dynaco Stereo 70 and PAS preamp sounded as good or better than anything I have ever used. That was 1963. Sure, the McIntosh amps were as good but also a lot more money. I definitely prefer tubes in any application where serious listening, especially with a good turntable, cartridge and a great pair of speakers are involved. Any stereo system is only as good as its weakest link. I am always looking for tube amps whether for my guitar or for my sound system. Vinyl records are still the ultimate source, in my book. The only major changes I make when re-building old tube amps are replacing the rectifier tube with a good solid state rectifier and replacing all of the old, worn, off spec caps and resistors with modern close tolerance improvements. No matter what the "specs" say, I know what I like; analog. Jim
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With all due respect, IMHO the "path of least resistance" would be to buy a decent condition used Sherwood or Dyna or any one of a dozen other brand integrated stereo tube amps, perhaps with a tuner in it...or not...either as a rebuild project or rebuilt, from an audiophile company where folks bring these things in, they rebuild them and resell them. Best would be to find something on your local Craigslist in nice shape, having been in one person's/family's possession for 50 years, buy it and re-cap it. If they need only modest power, say 15 watts, there are millions of these things out there running EL84's.
Yeah, I know, that doesn't sound like much of a project. But it won't cost you any more than you are likely to spend and will require roughly 80 hours less effort when you count sourcing the parts, building, and chassis work. The chassis is done, the concentric knobs are done, the rubber feet are done, the transformers are done. The input-switching is done, probably you get a tuner. There is already a manual for it.
I don't mean to be a party pooper. In rebuilt with guarantee condition you might pay $450 for such a thing, EL84-powered, if you're being brutallly overcharged. Maybe $600 for 6L6/7591/EL34 power. That's from a retail stereophile store. Subtract $150 from an individual. In 2015, to buy the transformers alone is gonna cost you in the neighborhood of $200.
My .02
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Eleventeen, of course. I emailed the lads some of my ideas this morning and mentioned that without really adding up every single part I thought it would cost about $1000. If that's too much for them I'll suggest the refurbish route.
Thanks for the suggestions everyone.
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(http://i172.photobucket.com/albums/w32/ttm4/eico_2_zpsl9std6ys.png)
Very decent, you could hardly buy the trannies for that much. That's not to say you couldn't get such a thing for $25 at a garage sale, too.
That particular seller, oceanview_hi has loads of these things all the time. In a lesser-desired brand than EICO, you might do better.
Link: (which will expire at some point) http://www.ebay.com/itm/Vintage-Eico-St40-Stereo-Tube-Integrated-Amplifier-For-Repair-Needs-Tubes/161609691506?_trksid=p2047675.c100009.m1982&_trkparms=aid%3D777000%26algo%3DABA.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Da6663118cc724ce3989dbc03f4187841%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D121593424630 (http://www.ebay.com/itm/Vintage-Eico-St40-Stereo-Tube-Integrated-Amplifier-For-Repair-Needs-Tubes/161609691506?_trksid=p2047675.c100009.m1982&_trkparms=aid%3D777000%26algo%3DABA.MBE%26ao%3D1%26asc%3D20131227121020%26meid%3Da6663118cc724ce3989dbc03f4187841%26pid%3D100009%26rk%3D1%26rkt%3D1%26sd%3D121593424630)
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> I'm not going to have to face all the caps north
West.
> IMHO the "path of least resistance" would be to buy a decent condition used
+1
Except in the 1980s you could buy these hunks mostly-working and the corrosion was not too bad. But many of these were VERY hay-wire and a real pain to work in. All these years later they are very sad, or very over-priced, or both.
The Hagerman designs are *excellent*.
I'm 50:50 about the Dynas but people like them and you can buy fresh new parts-kits for reasonable prices.
> IT guys at work
> These guys aren't audiophiles
How over-paid are your IT people?? (This is a sore-spot for me...)
Do they really need/expect an ALL TUBE system?
And is this for the IT office?
IMHO, a tube phono preamp is just constant trouble. First to get it hum-free. Then after you put it in the home, the tarnish on the pins is constant crackles and cut-outs. And tubes will go hissy "for no reason". All of this is 10X worse than your guitar amps because of the lower signal levels. One of the first things I did when semiconductors got not-crappy was get the tubes out of my low-level stages. (Yes, a few of the BEST tube phonos were really good for many years.)
Since I said that Hagerman is cool, I send you back for his op-amp phono preamp. It is really excellent. And less cost and much less trouble than a tube phono. I'd do the line-amp in chips too.
If this is for the office, they can't be using 150 Watt sweep-tube power. Even after 5pm they may get complaints from a few Watts. I'd take the back-end of the AA-Champ, twice. One 12AX7 and two 6V6, two OTs, a pinch of NFB. It is genuine tube sound, and heat and glow, it is common parts, it will cover the range of non-special loudspeakers, and it will push several % THD which makes it different from whatever they would find at Best Buys or Circuit-Cellar.