You could always go for a hybrid amplifier.
I have seen hybrids upto 900watts peak.
Speakers of that kind of efficiency will also reveal noises farther up the signal chain that you'd never hear with lower-efficiency ones...I know I've gone through some preamps on 96dB/W speakers that other people haven't heard anything wrong with on more traditional designs.
You can build a tube amp with a multimeter and a soldering iron. A scope, a function generator, and a variac are nice to have, but not required to get started. An additional multimeter may also be handy when bringing the amp up but not required. You will use the voltmeter to check your B+ voltage and adjust the bias of the output tubes when getting the amp up and running, among other things.
The various ST-70 kits around use different driver topology and tubes, I'm no expert here, but a search will most likely turn up some good info. Again, once built, plenty of tinkering opportunity for trying different driver boards, etc. There is also a dedicated ST-70 forum over at diytube.com :: Index IIRC, there is a kit available for sale over there also.
Use good solder, it makes things easier. There are a few people on ebay selling 20' of Cardas quad-eutectic solder for around $5 shipped, plenty to do a couple of amps. The stuff melts and flows like butter, and you'll be chasing less cold joints later.
It's nice to bring the voltage up slowly when first firing a newly-built project up. Without a variac, you can accomplish this with a lightbulb in series with the power cord. Search the forum for details.
Remember, tubes operate at high voltage, and can be dangerous/lethal. The B+ voltage in an ST-70 kit or similar PP amp is around 400V give or take a little, and this voltage needs to be treated with respect, like using clip leads (highly recommended) on your meter for hands-off testing. If you must probe a live amp always stick one hand in your pocket (use a clip lead on the neg side of the meter). Put bleeder resistors across the HV power supply caps to allow the high voltage to bleed off when the amp is powered down. I imagine modern kits include these.....
Read the sticky on safety at the top of this forum for other tube safety basics.
If you've got a little soldering/electronics experience, an ST-70 kit is a fine first project. It also can be modified over time so it can keep your interest for awhile.
""No such thing"" ???
Let me get this right.... your wanting a relative noobie to do an ST-70 kit??
He'll get lost just in the part count! K.I.S.S. Try this one from 'Andreas'" schematics listings.....
Class A, really simple....just to get his feet wet. The idea of running a full PP is just asking for him to get discouraged. Besides.... kits really take away the real "fun", point to point wiring, the layout, dimensions......all the real good stuff.
_____________________________________________________Rick....
Let me get this right.... your wanting a relative noobie to do an ST-70 kit??
He'll get lost just in the part count! K.I.S.S. Try this one from 'Andreas'" schematics listings.....
Class A, really simple....just to get his feet wet. The idea of running a full PP is just asking for him to get discouraged. Besides.... kits really take away the real "fun", point to point wiring, the layout, dimensions......all the real good stuff.
_____________________________________________________Rick....
Attachments
The OP asked for a kit. He also wants to keep his speakers. The speakers rule low power SE circuits out. More than 1 ST70 has been successfully assembled by somebody "following the dots".
The tubelab kits, although not for this application, were a great learning experience for me. Gave me the opportunity to learn how to calculate values, and then see the answer. Most importantly the success at then end.
While I agree P2P is really fun and an adventure, a kit is a good place to start. Too bad George's PP board isn't ready for press yet.
While I agree P2P is really fun and an adventure, a kit is a good place to start. Too bad George's PP board isn't ready for press yet.
The classic Dynakit kits were about as foolproof as it comes. The new ones are only better.
ST-70 Assembly Instructions
There are an abundance of pictures in the assembly manual. Not much can go wrong.
Add to the fact that the ST-70 has a huge number of followers and the amount of support available for that amp is second to none.
OK,...OK..........15.94 MB of instructions??????
Nearly Sixteen Mega-bytes of instructions? Even the word Mega....shouldn't be in a tube lovers vocabulary...except for frequencies we are trying to filter out.
That was enough time for me to scrub down the living-room floor.
Thirty two pages of instructions.
And, and SMDs' ????? "Daddy?... were you born when S M Ds' came out"??
So how much of a time gap is that....when the ST-70 came out & SMDs arrived?
What was that saying about a silk purse & a Sows ear?
Really.... I'm NOT trying to still up the pot....with so MANY choices lets think up some more examples. What does George have that would be suitable?
________________________________________________________Rick.....
Nearly Sixteen Mega-bytes of instructions? Even the word Mega....shouldn't be in a tube lovers vocabulary...except for frequencies we are trying to filter out.
That was enough time for me to scrub down the living-room floor.
Thirty two pages of instructions.
And, and SMDs' ????? "Daddy?... were you born when S M Ds' came out"??
So how much of a time gap is that....when the ST-70 came out & SMDs arrived?
What was that saying about a silk purse & a Sows ear?
Really.... I'm NOT trying to still up the pot....with so MANY choices lets think up some more examples. What does George have that would be suitable?
________________________________________________________Rick.....
Not quite that old !
I used to program for a company on a Sinclair Spectrum and microdrives !
Clive Sinclair once said 48K would be the most anyone would ever need !
I have the power supply from an old 5 Meg Winchester Drive that weighs nearly 100lbs. I use it as power supply for my foam cutter. iirc the platters were 24" in diameter.
Yes we had to use punch cards to enter the programs. We were allowed to use the terminals only after we mastered cards. It was a transistor computer though.
I am not saying the st70 is the amp to build, but I guess if one was REALLY against SMD's then just replace them with a axial type.
Yes we had to use punch cards to enter the programs. We were allowed to use the terminals only after we mastered cards. It was a transistor computer though.
I am not saying the st70 is the amp to build, but I guess if one was REALLY against SMD's then just replace them with a axial type.
AFAIK, George does not yet have a "Simple PP" to sell.
I agree with the comments disparaging SMD parts for DIY purposes. The Triode Electronics ST70 driver board is all through the hole mounting. After some practice, to get the soldering skills up to snuff, the OP should be able to stuff the board and take care of the point to point work needed to complete the project. A 25 W. or so "Rat Shack" iron, along with 63/37 SnPb eutectic alloy/RA flux solder, rates to be satisfactory.
The understandable decision to retain the Polk speakers drives everything else. Speakers 1st, then an amp is proper procedure.
The OP asked about kits. If a scratch build was being entertained, I'd suggest "El Cheapo" style circuitry using 7591 O/P tubes. Power O/P is adequate, the circuitry is comparatively simple, and a separate control center is not needed. Look at the 7591 data sheet. IMO, the "fixed" bias/ultralinear operating conditions set is noteworthy. High bang for the buck Edcor CXPP60-4-6.6K O/P trafos would be used. It's too bad Edcor doesn't offer a model CXPP60-6-6.6K, as that would be "perfect".
This is a nice high quality PP EL84 12wpc.
2 x 12 watt ultralinear EL84/6P14P power amplifier.
2 x 12 watt ultralinear EL84/6P14P power amplifier.
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