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Old 29th October 2011, 03:39 PM   #321
M Gregg is offline M Gregg  England
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Must stop posting.

Last one!

6Hrs again ....

Al DiMeola Electric Rendezvous

Al DiMeola - Cruisin' - YouTube

http://www.youtube.com/watch?v=np3Qr...feature=fvwrel

Regards

M. Gregg
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Old 30th October 2011, 03:14 PM   #322
Alastair E is offline Alastair E  Wales
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Sounds like you're enjoying it M-Gregg....

I'm still messing round, Ive made up some 'CCS' (MOSFET Anode-Load boards), but as the volts from them is approx 1/2 +B to allow the best op-point of the SN7 before the phase-splitter, I must use a pot. divider or modify the P.I. for self-bias, to keep the P.I. bias point right.....

I prefer the pot. divider idea,--two caps in the gain-stage is quite enough IMHO! although this will lower the loop-gain by a few dB....

--Hey M-Gregg, We may have a use for those 6SL7 you have after all!
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Old 30th October 2011, 08:44 PM   #323
Alastair E is offline Alastair E  Wales
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Well, Ive done this last modification.

Ive now got MOSFET loaded second gain stage, with a pot. divider to maintain correct bias for the P.I. as its still DC coupled.

First impressions, sound is a tad 'richer' and bass appears to extend further down,--less 'cramped'...

Clarity is superb, and there doesnt appear to be much in the way of lost gain, probably due to the action of the 'Mu stage', the effective amplification-factor is now closer to the theoretical max of 20 for the SN7, whats lost in the pot. divider is sorta partially compensated for.

Much more listening before I decide whether this mod is worth it, but first impressions are good....
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Old 30th October 2011, 11:19 PM   #324
M Gregg is offline M Gregg  England
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Quote:
Originally Posted by Alastair E View Post
Well, Ive done this last modification.

Ive now got MOSFET loaded second gain stage, with a pot. divider to maintain correct bias for the P.I. as its still DC coupled.

First impressions, sound is a tad 'richer' and bass appears to extend further down,--less 'cramped'...

Clarity is superb, and there doesnt appear to be much in the way of lost gain, probably due to the action of the 'Mu stage', the effective amplification-factor is now closer to the theoretical max of 20 for the SN7, whats lost in the pot. divider is sorta partially compensated for.

Much more listening before I decide whether this mod is worth it, but first impressions are good....
Should be interesting!

......

Regards
M. Gregg
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Old 31st October 2011, 07:21 PM   #325
atmasphere is offline atmasphere  United States
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Originally Posted by M Gregg View Post
Well yes you are correct,

I have the replacement tube for the original 6H8C.

The sound is way better. So their you go. Tung Sol's on order.

Regards
M. Gregg
You want to watch it with **any** of the Russian-made 6SN7s. So far the Tung Sols have shown a lot of leakage, although they sound OK if leakage is not a problem in your amp (meaning that you have regulated DC supplies for the 6SN7 filaments...).

The vintage Russian 6SN7s are another matter- by 'vintage' meaning 1970s or earlier. They can be excellent.
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Old 31st October 2011, 09:12 PM   #326
M Gregg is offline M Gregg  England
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You want to watch it with **any** of the Russian-made 6SN7s. So far the Tung Sols have shown a lot of leakage, although they sound OK if leakage is not a problem in your amp (meaning that you have regulated DC supplies for the 6SN7 filaments...).

The vintage Russian 6SN7s are another matter- by 'vintage' meaning 1970s or earlier. They can be excellent.
Thank's for the information,

I have regulated supplies for heaters on the input 6SN7's.
I have a vintage (NOS) Brimar in the phase splitter (AC Heater).
The ones I am using on the input at the moment are 1960's russian.

What do you regard as the "Best" 6SN7?

Regards
M. Gregg
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Old 31st October 2011, 09:12 PM   #327
Alastair E is offline Alastair E  Wales
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Perhaps I was just lucky with my 'fake' tung-sol tubes....

They perform flawlessly and have no leaks...
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Old 31st October 2011, 09:15 PM   #328
M Gregg is offline M Gregg  England
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Perhaps I was just lucky with my 'fake' tung-sol tubes....

They perform flawlessly and have no leaks...
Liquid cooling..LOL

I'm wonder if Mr murre has his toroids yet?

When are you going to start the Mark 2 build?

Regards
M. Gregg

Last edited by M Gregg; 31st October 2011 at 09:20 PM.
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Old 31st October 2011, 09:34 PM   #329
Alastair E is offline Alastair E  Wales
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Liquid cooling..LOL

I'm wonder if Mr murre has his toroids yet?

When are you going to start the Mark 2 build?

Regards
M. Gregg
Well,--TBH, It will probably be a while....

I havent a lot of time lately--or spare dosh-- for the build...

Probably end up after Christmas before I start it properly....
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Old 31st October 2011, 09:44 PM   #330
atmasphere is offline atmasphere  United States
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Thank's for the information,

I have regulated supplies for heaters on the input 6SN7's.
I have a vintage (NOS) Brimar in the phase splitter (AC Heater).
The ones I am using on the input at the moment are 1960's russian.

What do you regard as the "Best" 6SN7?

Regards
M. Gregg
The 1960s Russian tubes are very nice. Most of the American 6SN7s are good too. Certain ones are sought after- the red base RCA, the metal base Sylvania 'Chrome dome' and the Ken Rad...

The Treasure tube sold by Grant fidelity in Canada is supposed to combine the best of the best features of the vintage tubes. I have enough reports from customers that basically say the same thing that I believe them now. However they are not cheap :/
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