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 Post subject: Re: Musician's Amplifier
PostPosted: October 16th, 2018, 7:43 pm 
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Posts: 159
Roscoe Primrose wrote:
Grover Gardner wrote:
About twenty years ago, I attended a listening session that featured Lowther speakers in fancy plywood boxes driven by single-ended 300B monoblocks built entirely with vintage Western Electric iron. About $12,000 there. Acoustic guitar sounded wonderful, Mahler not so much. The wine was flowing and in the middle of the session, our host for some reason plucked a $2000 1950's WE 300B out of one of the amps--he was going to make some point about the construction, I believe--and bobbled it. The rest of us watched it fly into the air...and drop on the hardwood floor. And I thought, that's not's going to be me. ;-)


I watched Vu's (ex I believe) wife pick up a boxed NOS 50 once and the bottom of the box came open.....

Roscoe


Ouch...


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 Post subject: Re: Musician's Amplifier
PostPosted: October 16th, 2018, 8:28 pm 
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Joined: June 4th, 2013, 2:39 pm
Posts: 159
Stuart Polansky wrote:
Hey Grover,

I'm putting together a set of Class A amps that can use any of the common octal output tubes: KT100, KT90, KT88, KT77, KT66, EL34, 6L6, etc., just so long as the pinout is the same.

My application will have two channels used from ~100Hz to 3.5kHz, the other from 3.5kHz up.

I can use different tubes in each of the four "channels". With the larger set of tubes, ~ 25WPC, the smaller ones ~15 WPC. I think even the 15WPC will be more than adequate.

Given your expertise, and what Charlie tells me are a great set of ears, what would your tube recommendation be? Price is an issue!

Thanks,

Stuart


Well, Russian 807s are $10 a piece. ;-) That's hard to beat. I haven't tried them but I plan to. I hear they're pretty good. If you want to do a "swappable" amp, use an octal socket and a set of 807 adapters you can get on eBay from China. The 807, KT66, 5881 and 6L6GC are interchangeable in this circuit. I'm *this* close to a WM5 anyway, which is 25 wpc, but that eliminates the 807--too much plate voltage. The suggested Russian 6L6 would also be an option.

Then there's the output transformer. I called Pacific and they can wind me another set of these 16309 repros for $200 a pair. They're not bad at all, they seem very stable and they're in spec for the W5M design. They'd probably be cheaper if I ordered more than two (hint). Not sure you'd find anything better for the money. With these, you could do a 12W triode and a 20-25W ultralinear. Just a suggestion. ;-)

The 15W triode Williamson called for 425-0-425 plate tranny. The W5M calls for 500-0-500, IIRC. Hammond makes both so thats doable. Maybe Edcors are cheaper, I don't know. For coupling caps you could use the Cornell-Dubilier 942 1000VDC series. They're damn good caps and cheap.

Does that help?


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 Post subject: Re: Musician's Amplifier
PostPosted: October 17th, 2018, 7:17 am 
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Joined: December 14th, 2013, 2:19 pm
Posts: 729
Thank you for the recommendations.

Stuart


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 Post subject: Re: Musician's Amplifier
PostPosted: October 17th, 2018, 4:46 pm 
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Joined: March 12th, 2013, 11:12 am
Posts: 529
That NOS 50 was half of a matching pair of Globe, NOS 50s in original green boxes! I got to hold the surviving one briefly, it was a beautiful tube!


Roscoe Primrose wrote:
Grover Gardner wrote:
About twenty years ago, I attended a listening session that featured Lowther speakers in fancy plywood boxes driven by single-ended 300B monoblocks built entirely with vintage Western Electric iron. About $12,000 there. Acoustic guitar sounded wonderful, Mahler not so much. The wine was flowing and in the middle of the session, our host for some reason plucked a $2000 1950's WE 300B out of one of the amps--he was going to make some point about the construction, I believe--and bobbled it. The rest of us watched it fly into the air...and drop on the hardwood floor. And I thought, that's not's going to be me. ;-)


I watched Vu's (ex I believe) wife pick up a boxed NOS 50 once and the bottom of the box came open.....

Roscoe


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 Post subject: Re: Musician's Amplifier
PostPosted: October 17th, 2018, 8:45 pm 
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Joined: June 4th, 2013, 2:39 pm
Posts: 159
Stuart Polansky wrote:
Thank you for the recommendations.

Stuart


You're welcome, hope it helps. I tried to build a simple, cheap no-feedback PP triode amp with beam tubes/pentodes. Never sounded good to me. These little Williamsons are another matter.

In 1952 the Navy tested a bunch of commonly available Williamson amps. The low-frequency capabilities were of interest to them in their sonar research. They were consistently blown away by the Peerless S-265-Q. With no alterations to the stock circuit, bandwidth and squarewave response were almost flawless. The Partidge WWFB got good marks, but the Patridge CFB, something of a holy grail for Williamson devotees, was disastrous. They tried two samples and a number of tweaks, and nothing helped. Poor bass response and above 10K it looked like a roller coaster. Interestingly, a low-cost Stancor did extremely well with the addition of a tuning cap across the feedback resistor. Another loser was the Acro TO-300. It rang like a bell above 10K and absolutely nothing they tried could get rid of it.

I guess I'll ask Mike LaFevre if he'll still make some S-265-Q's on special order. Probably cost an arm and a leg. But it appears to be the hands-down OPT of choice for a triode Williamson design.


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 Post subject: Re: Musician's Amplifier
PostPosted: October 17th, 2018, 10:25 pm 
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Joined: March 12th, 2013, 11:12 am
Posts: 529
Do you know how the TO-330 faired?



Grover Gardner wrote:
Stuart Polansky wrote:
Thank you for the recommendations.

Stuart




You're welcome, hope it helps. I tried to build a simple, cheap no-feedback PP triode amp with beam tubes/pentodes. Never sounded good to me. These little Williamsons are another matter.

In 1952 the Navy tested a bunch of commonly available Williamson amps. The low-frequency capabilities were of interest to them in their sonar research. They were consistently blown away by the Peerless S-265-Q. With no alterations to the stock circuit, bandwidth and squarewave response were almost flawless. The Partidge WWFB got good marks, but the Patridge CFB, something of a holy grail for Williamson devotees, was disastrous. They tried two samples and a number of tweaks, and nothing helped. Poor bass response and above 10K it looked like a roller coaster. Interestingly, a low-cost Stancor did extremely well with the addition of a tuning cap across the feedback resistor. Another loser was the Acro TO-300. It rang like a bell above 10K and absolutely nothing they tried could get rid of it.

I guess I'll ask Mike LaFevre if he'll still make some S-265-Q's on special order. Probably cost an arm and a leg. But it appears to be the hands-down OPT of choice for a triode Williamson design.


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 Post subject: Re: Musician's Amplifier
PostPosted: October 17th, 2018, 11:06 pm 
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Joined: June 4th, 2013, 2:39 pm
Posts: 159
[quote="TubeDriver"]Do you know how the TO-330 faired?[/quote+"TubeDriver"]

It was not among those tested. The candidates were McIntosh 20, 50 and 100 wpc, a Scott 221 (which they found irredeemably poor), a handful of Williamson triode circuits including the Stancor kit, a Craftsman and some long-gone brands, and a few ultra-linear Williamsons. You can google "navy williamson test" and see the results. It's very interesting.

I've read elsewhere that the Acros are not all they're cracked up to be and very circuit-specific. I have a pair of the TO-330s myself. The Acro catalogue features a PPP 807/KT66 schematic that's rather tempting. ;-)


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 Post subject: Re: Musician's Amplifier
PostPosted: October 17th, 2018, 11:16 pm 
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Joined: June 22nd, 2013, 11:00 am
Posts: 542
Roscoe Primrose wrote:
Grover Gardner wrote:
About twenty years ago, I attended a listening session that featured Lowther speakers in fancy plywood boxes driven by single-ended 300B monoblocks built entirely with vintage Western Electric iron. About $12,000 there. Acoustic guitar sounded wonderful, Mahler not so much. The wine was flowing and in the middle of the session, our host for some reason plucked a $2000 1950's WE 300B out of one of the amps--he was going to make some point about the construction, I believe--and bobbled it. The rest of us watched it fly into the air...and drop on the hardwood floor. And I thought, that's not's going to be me. ;-)


I watched Vu's (ex I believe) wife pick up a boxed NOS 50 once and the bottom of the box came open.....

Roscoe


Was that the reason for the divorce?

:|


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 Post subject: Re: Musician's Amplifier
PostPosted: October 18th, 2018, 3:45 pm 
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Joined: March 12th, 2013, 11:12 am
Posts: 529
I have heard a few DIY designs using TO-330 and they all sounded very good. I have *heard* the 330 is the one you want, the 300 is not nearly as good.



Grover Gardner wrote:
TubeDriver wrote:
Do you know how the TO-330 faired?[/quote+"TubeDriver"]

It was not among those tested. The candidates were McIntosh 20, 50 and 100 wpc, a Scott 221 (which they found irredeemably poor), a handful of Williamson triode circuits including the Stancor kit, a Craftsman and some long-gone brands, and a few ultra-linear Williamsons. You can google "navy williamson test" and see the results. It's very interesting.

I've read elsewhere that the Acros are not all they're cracked up to be and very circuit-specific. I have a pair of the TO-330s myself. The Acro catalogue features a PPP 807/KT66 schematic that's rather tempting. ;-)


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 Post subject: Re: Musician's Amplifier
PostPosted: October 18th, 2018, 8:54 pm 
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Joined: June 4th, 2013, 2:39 pm
Posts: 159
[quote="TubeDriver"]I have heard a few DIY designs using TO-330 and they all sounded very good. I have *heard* the 330 is the one you want, the 300 is not nearly as good.

That's good to know. I built an Eico HF-60 clone and it was very good. Were these no-feedback designs?


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