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.
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.
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
http://www.diyaudio.com/forums/tubelab/157491-pictures-your-tubelab-amp.html
Tubelab Home
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
http://www.diyaudio.com/forums/tubelab/157491-pictures-your-tubelab-amp.html
Tubelab Home
I might suggest SET 6DJ8 (or EF86 triod strapped) + EL84 triod strapped. OT is the most critical part of a SET.
http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey.html
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
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
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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.
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.
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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......
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
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
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'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.
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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.
Yes the sony's are a 3-way design with a fairly complex crossover. Darn! I spent all afternoon researching the tubelab simple se. I have hears before that a single ended low power amp may not work great with a speaker that has a complex crossover, but one bad could it be 😀. Any other thoughts on this?
Now off to research the el cheapo a bit. Thanks for all the responses!
Now off to research the el cheapo a bit. Thanks for all the responses!
As a first build I would also recommend the 30W schematic in the RCA 1974 Recieving Tube Manual, pp694-695. It can be downloaded here Tube Data. The 7868's in the output stage can be substituted with 6L6's or even 6BQ5's if you change the screen resistor. The 7199 in the pre-amp stage keeps the layout compact and they're readily available from tubedepot pretty cheaply and are under the radar for hobbyists so good replacements will be available for a long time. As far as iron goes, don't forget Magnetic Components in Chicago either. I think they're the best value for your money out there.
Would recommend staying with a PP design. You'll get more output for the same space/price and as far as a first project goes, it's more satisfying to shake the drywall with a mildly perceptible amount of pink noise than to have to listen hard for a moderate volume system with crystal sound. It's tubes... we're in it for the organic feel of the process anyway and a little harmonic distortion gives character.
Would recommend staying with a PP design. You'll get more output for the same space/price and as far as a first project goes, it's more satisfying to shake the drywall with a mildly perceptible amount of pink noise than to have to listen hard for a moderate volume system with crystal sound. It's tubes... we're in it for the organic feel of the process anyway and a little harmonic distortion gives character.
Casper: Following Eli & Jim McShane's recommendations, here are a couple of additional 12-15W PP amps with feedback: (Gingertube's BH was already mentioned above)
http://www.diyaudio.com/forums/tubes-valves/81492-red-light-district-another-pp-el84-amp.html
http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey.html
The BH is running in UL mode, and the RLD is running pentode. There are two versions of the BH build; one is cathode biased and the other is fixed bias with mosfet followers. If you decide to build this, I would suggest the fixed bias design. I've built the original cathode bias version, and I have the parts to convert it to the fixed bias mosfet design, just haven't got to it yet.
Both of these are EL84 amps, same output tubes as the Dynaco ST-35. BTW, the Edcor transformer that Eli linked to has UL taps and 16 ohm taps, so it offers a lot of flexibility. If you build a pentode design, you just leave the UL taps disconnected.
http://www.diyaudio.com/forums/tubes-valves/81492-red-light-district-another-pp-el84-amp.html
http://www.diyaudio.com/forums/tubes-valves/72536-el84-amp-baby-huey.html
The BH is running in UL mode, and the RLD is running pentode. There are two versions of the BH build; one is cathode biased and the other is fixed bias with mosfet followers. If you decide to build this, I would suggest the fixed bias design. I've built the original cathode bias version, and I have the parts to convert it to the fixed bias mosfet design, just haven't got to it yet.
Both of these are EL84 amps, same output tubes as the Dynaco ST-35. BTW, the Edcor transformer that Eli linked to has UL taps and 16 ohm taps, so it offers a lot of flexibility. If you build a pentode design, you just leave the UL taps disconnected.
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So many options! I like the baby huey build because there seems to be quite a bit of resources for it. Are there any PP amps that use a PCB instead of point to point? That is one of the things that attracted me to the tubelab stuff in the first place.
SY's RDL can cope well with LS. Mine are less then 90dB/W on Wifas and in 27 square meter room they loud enough and good sounding.
So build an ST-35 from scratch. You can buy a really good transformer set from Triode Electronics and "Dirty Dawg" amps has chassis for $15. Use an over sized chassis and turret type contraction and it will be very easy to modify. But it will not look anything like an ST-35. For a first amp, the layout will be so much easier if you use a larger chassis size
here is an example of a turret type board I was working on. It is not fully populated (You can see the empty turrets.) It is being test fit for the first time in a chassis. You can see it is easy to swap parts even years later. You don't need a PCB to build an ST-35
But with 98dB speakers you could build a single ended design. These have one less tube per side but use bigger transformers. The stretch built st-35 would be a conservative option. It is a VERY well known design.
All that said, the best first project is a guitar amp. They are only one channel and can be very simple
What is the actual measured resistance of the loudspeaker at the crossover input?
Yes, the tubelab simple PP........uses EL84 outputs. This is the latest design from Tubelab George and a PCB is available.
There are a few posts here about the simple PP in the Tubelab vendor forum.
Here is a big one...http://www.diyaudio.com/forums/tubelab/148694-tubelab-simple-p-p.html
Simple P-P
The Edcor model CXPP25-MS-8K O/P trafos that Eli recommended earlier would be an excellent choice for any of these EL84 PP designs (BH, RLD, El Cheapo (12AQ5), Simple PP, ST-35 clone, etc)
If the budget allows, the James JS-6228H would also be appropriate. Some sites show a 16 ohm tap for this model, it's probably a good idea to confirm before pulling the trigger on these.
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