First Tube Build, Thoughts?

[Casper222]

So I am almost through the tube section in the NEETS course and am starting to feel like I am getting a grasp on the theory behind tubes. As I continue my reading through other sources I was wondering if I could get some insight on what would be a good first project to start.

I am looking to build a power amp for a set of Sony SS-3300 speakers. They are quite efficient at 98db/1w/1m and are a 16 ohm impedance. What would you suggest be a good fit for such speakers? More complete speaker specs are here: Sony SS-3300 on thevintageknob.org.

I have toyed arround with the idea of just ordering the Dynaco ST-35 kit from tubes4hifi. But I kind of like the challenge of building something from scratch. So any newby friendly designs would be much appreciated. I would be working with a budget of around $700-$800 all in.

Thanks in advance for your responses.

[REDHORSEMAN]

How about this one?
KT88 SE Basic or Master Kit

[boywonder]

Very cool speakers!

A couple of watts is all you will need at 98db sens.

It appears that your budget will support a Tubelab SE or (easily) a Tubelab Simple Single Ended.

The Tubelab SE is a fixed bias DHT design with mosfet followers, and can utilize tubes like 300B (8W or so), the 2A3, and the 45 (2W or so)

The Simple Single Ended is a cathode bias design that you can run in triode or ultralinear mode using common output tubes like EL34, KT88, 6L6GC, 6V6, etc. for anywhere from 2W-12W or so.

Tubelab George sells PCBs for either design for $35+shipping or you can do a point to point build.

There is loads of support here for both of these designs:

Tubelab - diyAudio

Pictures of your Tubelab amp

Tubelab Home

[suntechnik]

I might suggest SET 6DJ8 (or EF86 triod strapped) + EL84 triod strapped. OT is the most critical part of a SET.

[Soonerorlater]

EL84 Amp - Baby Huey

The first part of the above thread is a very good read ( as is the rest if you have time to read it all.... ). There's a lot of practical help in the choice of actual components used in this push/pull amp putting meat on the bones of theory.

Furthering Suntechnik's advice,



RH 84 - Tube Audio ...... RH DESIGN

There are many threads on this forum giving help on how to build the RH84, a popular single ended design.


HTH Bill

[Mr. Zenith]

Having 98db speakers gives one lots o' options. I'm running an RH84 into a pair of Klipsch RF-3's, and it performs quite admirably. It absolutely amazes people that there's less than 4 watts at play!

That said, suntechnik was spot-on about the OPT's. You can get some pretty good ones (Edcor leaps to mind) for not much money, but get good ones if you can afford it. I broke the bank for a pair of James OPT's and have never regretted it.

[boywonder]

Originally Posted by Mr. Zenith

That said, suntechnik was spot-on about the OPT's. You can get some pretty good ones (Edcor leaps to mind) for not much money, but get good ones if you can afford it. I broke the bank for a pair of James OPT's and have never regretted it.

Sounds like the budget may support a pair of James Transformers; my Tubelab SE 300B is using James 6123HS and it's booted everything else out of my main system for a few months now (running 95db FR speakers). I'd consider a 45 SE amp with James or Electraprint transformers. With 45 tubes, you can probably use the James 6113HS.

OTOH, getting James in 16 ohm may be tricky; you can custom order Electraprint in 16 ohm pretty easily I imagine......so perhaps a 45 based amp with 16 ohm Electraprints......

[KrankKall]

I built a standard RH amp SE (12AT7/EL84) and an all-Octal RH84 amp SE (6SL7/6V6).
The standard RH84 SE amp runs a pair of Heybrook HB1's, while the Octal RH84 SE amp runs a pair of ADS L-10's.
Neither speaker is anywhere close to being 98db eff., yet they can get extremely loud on only 4-5 watts per channel.
Both amps used Edcor power and output transformers, inexpensive but well-made.

Steve

[Eli Duttman]

It seems people paid attention to the 98 dB. sensitivity of the Sony speakers, without noticing that they are a (sic) 3 way design. That means the crossover must be at least somewhat complex. Complex crossovers and low power, no NFB, SE amps are not "a marriage made in heaven".

I'll grind my own axe and suggest the OP build an "El Cheapo". He'll have all the power needed, along with a better damping factor than that delivered by a no NFB design. The "icing on the cake" is that he will have money left over from the budgeted amount to use in buying recordings. Also, no preamp is needed if a "standard" CDP is the signal source.

Build with Edcor model CXPP25-MS-8K O/P trafos. Use the 16 Ω tap for the speakers, the 8 Ω taps for the NFB connections, and tie the 4 Ω taps off.

You really can't get the B+ high enough using just the N-77U. That's why the latest power "iron" recommendation is a Triad N-77U for main B+, a Triad VPS24-1800 for "12" V heater power and B+ boost, a Triad C-24X B+ filter choke, and an Allied 6K27VF for 12AT7 heater power and B-. Buy all of 'em at once from Allied and save on shipping costs.

Jum McShane is the source for the tubes and small parts needed to execute the design. Jim did some mighty careful scrounging to assemble decent parts at a modest cost.

Given the presence of decent O/P "iron", the high pass filter combo of 56 nF./100 KOhms can be safely changed to 68 nF./120 KOhms. Doing so places the amp's low freq. limit below 20 Hz.

[Jim McShane]

Originally Posted by Eli Duttman

It seems people paid attention to the 98 dB. sensitivity of the Sony speakers, without noticing that they are a (sic) 3 way design. That means the crossover must be at least somewhat complex. Complex crossovers and low power, no NFB, SE amps are not "a marriage made in heaven".

I'll grind my own axe and suggest the OP build an "El Cheapo". He'll have all the power needed, along with a better damping factor than that delivered by a no NFB design. The "icing on the cake" is that he will have money left over from the budgeted amount to use in buying recordings. Also, no preamp is needed if a "standard" CDP is the signal source.

Build with Edcor model CXPP25-MS-8K O/P trafos. Use the 16 Ω tap for the speakers, the 8 Ω taps for the NFB connections, and tie the 4 Ω taps off.

You really can't get the B+ high enough using just the N-77U. That's why the latest power "iron" recommendation is a Triad N-77U for main B+, a Triad VPS24-1800 for "12" V heater power and B+ boost, a Triad C-24X B+ filter choke, and an Allied 6K27VF for 12AT7 heater power and B-. Buy all of 'em at once from Allied and save on shipping costs.

Jum McShane is the source for the tubes and small parts needed to execute the design. Jim did some mighty careful scrounging to assemble decent parts at a modest cost.

Given the presence of decent O/P "iron", the high pass filter combo of 56 nF./100 KOhms can be safely changed to 68 nF./120 KOhms. Doing so places the amp's low freq. limit below 20 Hz.

I agree with Eli - the need for a better damping factor is real. El-Cheapo is a very good choice - the modest NFB helps a lot in the damping department. And if need be the LF bandwidth can be limited at the input with a simple cap change that happens outside the NFB loop.