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Re: but, but, but... [message #31101 is a reply to message #31100]

Sun, 22 May 2005 02:00

Damir
Messages: 1005
Registered: May 2009

Illuminati (2nd Degree)

Yes, we need 3Vrms at the input for full output (about 2*60Vrms), but I mentioned 2Vrms like "desirable" input sensitivity (max. CD output).
We`ll definitely need a preamp... something like "Guinevere"?

P.S. how you guys solved input switching, (cheap) volume pot problems, etc.? I looked at the some commercial stepped attenuators and input switches, but the price...

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so then.... [message #31102 is a reply to message #31101]

Sun, 22 May 2005 07:27

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

With an 8k a-a, B+ can be 360 V, plus 75-80V of cathode bias, and B+:ground can be 450. No problem getting a 200v p-p swing( per plate ) out of a supply like that. Go to 10k a-a and we can be absolutely sure of Class A operation if bias is in the 80-90 mA area.

Use a CCS instead of a resistor, or perhaps an unbypassed R for the cathodes. I suspect the R will give better overload performance than the CCS.

I'd rather build a low gain pre like Guinevere with 12B4's and roll a bit of gain into the adjustable volume control/buffer stage. Or take 12B4's and keep the 5687 gain of Guinevere. there is something to be said of two stage amps and linestages with gain. Work together on system requirements instead of building the whole thing to a specific standard of sensitivity( which will set limits on tube choice somewhere in the chain...).
regards,
Dogulas

Praise the Lord, and pass the 813's!

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Re: so then.... [message #31103 is a reply to message #31102]

Mon, 23 May 2005 18:01

Manualblock
Messages: 4973
Registered: May 2009

Illuminati (13th Degree)

O'Kay; so whats next? Doug; when will you be settling on an amp to exhibit these thought experiments.

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Re: so then.... [message #31104 is a reply to message #31103]

Mon, 23 May 2005 19:08

PakProtector
Messages: 935
Registered: May 2009

Illuminati (2nd Degree)

Hey-Hey!!!,
I am building a pair of monoblocks with 4E27 finals. It is a valve somewhere between a HY69 and an 813 in ratings and dissipation limits. L-C power supply of between 600 and 700 volts. Current delivery of ~300 mA. Ultra-Linear rigging of the finals and E-Linear front end. Cascode differential amp like Merlin. I am not exactly sure how the finals like their U-L connection, so I will be fairly sure of getting where I want to be with those options.

I need to get paid a few times before I order the Iron, but I don't think anything will change very much. I have been fairly sure of this design for a bit now. It's just a matter of scale, those OPTx's would be just as happy with a pair of EL84's as 845's.

Still need to decide upon the specifics of the cascode front end, there are quite a few options. I will be posting notice before ordering the OPTx's so as many folks as possible can throw in their money and net us a good price on a bigger run of them.
regards,
Douglas

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