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Old 6th October 2009, 03:40 AM   #101
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Heya Jeff,

Quote:
Originally Posted by vinylkid58 View Post
Old school integrated, not the greatest schem: http://www.triodeel.com/eist70ps.gif

Looks like decent iron?
Ooooookay, one of them things... 7591... yeah, 6K6 OPT.

Thanks for the info

Cheers!
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Old 6th October 2009, 06:32 AM   #102
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I have a fully restored Eico ST-70 with some recommended enhancements from David Gillespie. I can say the irons are indeed quite decent. These 2 are from another ST-70 that I picked up from a garage sale.

Since these OPT don't have UL tap, this amp from Pete and Miles 6BQ6GTB/807 pentode are my final choices. Pete's PCB makes the build a lot easier, but the 6BQ6GTB and the 807 tube are close to the 7591 which are the OPT was designed for. Tough choice.
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Last edited by pchw; 6th October 2009 at 06:45 AM. Reason: I meant 6BQ6GTB, not 6BG6.
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Old 6th October 2009, 09:37 PM   #103
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Hi Fred,

Quote:
Originally Posted by pchw View Post
...but the 6BQ6GTB and the 807 tube are close to the 7591 which are the OPT was designed for. Tough choice.
I know the 806 likes much as the 6L6 family does, but I thought Miles was using 4400 ohms A-A for his 6BQ6 beauty?

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Old 7th October 2009, 01:53 AM   #104
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Quote:
Originally Posted by Geek View Post
Hi Fred,I know the 806 likes much as the 6L6 family does
Huh? I guess you must have meant 807 there. The 806 is something much different.

Quote:
I thought Miles was using 4400 ohms A-A for his 6BQ6 beauty?
That's what it does use: 4K4 (P-2-P). Given the plate characteristics, a 6K6 (P-2-P) would put you way down on the characteristic, and away from the most linear part. 6K6 would probably be more apropos to much higher voltages and Class B or Class C for an RF amp.

There was one Portugese (Brazilian?) deisgn for an AM plate modulator that got 70W of audio from a PP pair of 6BQ6GTBs, but it was deep into Class AB, and definitely not designed with sonic excellence in mind (which is not legal on the ham bands anyway).
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Last edited by Miles Prower; 7th October 2009 at 01:57 AM.
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Old 7th October 2009, 05:54 AM   #105
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Quote:
Originally Posted by Miles Prower View Post
Huh? I guess you must have meant 807 there. The 806 is something much different.
My bad... my brain was two tabs over from when I posted

Now I have some 4.3K-ish Dynaco iron here, I can play with your design some


Cheers!

Last edited by Geek; 7th October 2009 at 05:59 AM.
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Old 7th October 2009, 06:06 AM   #106
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Bummer, but I do have a pair original Dynaco ST-70 OPT's that are .... 4.3K P-2-P? If so, I am still in the game
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Old 7th October 2009, 08:24 AM   #107
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Yes you are!

PP isn't squeamish about being loaded heavier.

Just go for lower voltage, more current and stay outta deep class-AB and you'll do 4.3K fine.


Cheers!

Last edited by Geek; 7th October 2009 at 08:26 AM.
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Old 7th October 2009, 02:34 PM   #108
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I'm trying to keep costs down. Would I be able to get away with a 820pf X5F ceramic instead of mica? I would expect that this has an anti-RF application and an X5F may not do well over 10Mhz?
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Old 7th October 2009, 03:30 PM   #109
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Quote:
Originally Posted by whitelabrat View Post
I'm trying to keep costs down. Would I be able to get away with a 820pf X5F ceramic instead of mica? I would expect that this has an anti-RF application and an X5F may not do well over 10Mhz?
I would expect the ceramic would do fine. I put the caps there because there was some tendency to oscillate if the OPT leads were very long - not sure exactly what the FB path was. Also tended to optimize the square wave response and damp any ringing. You may not even need them...

Pete
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Old 8th October 2009, 02:53 AM   #110
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Quote:
I can't find any 10uF 500v electrolytics .... I have a 47uF 500v Panasonic that seems to fit.....Scratch that. The 47uf is a 450v, not 500v
Quote:
862-6216 100uF 500V $2.31 Still shows 17 in stock, but I ordered 10 this morning.
I got these today, they are tall and skinny, and they fit the board just fine. Unfortunately, now they are all sold out!

Quote:
862-6214 82uF 500V $2.03
I got some of these too, but they are short and fat and cover up some surrounding components. They will work in a low profile version of the Simple P-P which is why I got them. I didn't order any other caps this time.
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