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Old 18th July 2018, 06:05 AM   #1301
Ralph G is offline Ralph G  Netherlands
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Quote:
Originally Posted by e_fortier View Post
Even cheaper option is the 159ZC, also open framed. I believe someone on this thread tried it at 2.5A (bias of big MoFo) with no ill effect.
That would be me. I use the 159ZC with a small IRFP250 and a big IXYS mosfet. I can switch between the two. The 250 is biased around 1.8A I think and the big IXYS around 2.3A.

It is currently very, very hot in Holland. I made this amp during winter in my basement. At that moment it was around 17C (63F). It is now close to 30C in my listening room (86F), so the amp is running a bit hot with the IXYS. Yesterday I switched the whole evening between the 2 Fets and biases and there is not a big difference. Maybe the IXYS with the higher bias has a bit fatter bass. Might be due to a little distortion. Don't know, don't care. I like the result.

One more thing: I read thinks about using huge inductors with low resistance. Why not go for a balanced version? Make 2 MoFo's per channel. Use 2 inductors with half the inductance (if I'm not mistaking). Lower the voltage and crank up the bias a bit. You could use the 159ZE with 3A and 15V. You would have a lot of power and you can even drop the output caps.

Problem can be driving this balanced version if you don't own a balanced pre amp. Finding a decent signal transformer for these high voltages is difficult.
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Old 18th July 2018, 06:58 AM   #1302
jostwid is offline jostwid  Switzerland
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Originally Posted by EmeryBB View Post
Thanks Jostwid, I'll order the 195T then. Postage is free actually.
As for being open framed, it doesn't matter does it?
"Pottet or not pottet" was once an article in "Soundpractices" magazine. Actually open frame is preferred by many when speaking about electrical and sound properties. Aesthetics are another question.

As for myself i would, like others mentioned already, go for the cheap 159ZC. The only reason to go for the 195T5 is to go to high amperage maybe when using a big IXYS part
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Old 19th July 2018, 02:18 AM   #1303
nikon f is offline nikon f  United States
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Could the battery powered Bottlehead Quickie be used with the Mofo?
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Old 19th July 2018, 02:33 AM   #1304
e_fortier is offline e_fortier  Canada
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One of Bottlehead moderator mentions that this preamp has a very low gain (7db)

Youll have sound but wont hear the full potential of the MoFo

My 2 cents
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Old 19th July 2018, 04:03 AM   #1305
drpro is offline drpro  United States
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I swinging my MoFo with the Aksa-Lender 40v preamp, a very nice combo.
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Old 19th July 2018, 05:58 AM   #1306
Ralph G is offline Ralph G  Netherlands
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Simple SRPP tube amp. I use a 6N6P. Close to ECC99 or 12BH7. No issues. Nice open sound. No stresssssss.

Cheap to build (if you can get russian tubes directly from Russia or a former Sovjet countrey ). I bought a box 6N6P from Moldavia and paid something like 40 dollars for a box of 20). All brand new Mil spec.
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Old 20th July 2018, 10:16 AM   #1307
Little_Eddy is offline Little_Eddy
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I'm proposing to use the MoFo with my valve pre having Sowter 9525 inter stage transformers with the output floating and not tied to the 0V rail, Niobium - Valve pre for SS Power Amp - audio-talk

Will I be able to bypass C1 as per the attached?18-07-20 MoFo Inter Stage Schematic.bmp
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Old 20th July 2018, 10:54 AM   #1308
316a is offline 316a  England
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Quote:
Originally Posted by Little_Eddy View Post
I'm proposing to use the MoFo with my valve pre having Sowter 9525 inter stage transformers with the output floating and not tied to the 0V rail, Niobium - Valve pre for SS Power Amp - audio-talk

Will I be able to bypass C1 as per the attached?Attachment 692751
It's hard to see on the schematic what you are intending . What you need to do is place the transformer secondary in series between the gate stopper and the bias circuitry of the the mosfet . I notice you have placed a load resistor on the IT secondary . Was this value derived according to the capacitance presented by the mosfet ?

316a
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Old 20th July 2018, 01:49 PM   #1309
Little_Eddy is offline Little_Eddy
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Originally Posted by 316a View Post
What you need to do is place the transformer secondary in series between the gate stopper and the bias circuitry of the the mosfet . I notice you have placed a load resistor on the IT secondary . Was this value derived according to the capacitance presented by the mosfet ?

316a
OK so if I wanted to have 2 inputs, I need to divert the bias voltage via the inter stage transformer with a switch. Potential scheme attached. Unsure whether the second set of switch contacts from inputs to the gate stopper is needed and seems like quite something just to get rid of C1.18-07-20 MoFo Inter Stage Schematic.bmp

Perhaps just be easier investing in a better C1 if I'm that bothered about it's sonic impact.

Or probably easier, just lift one end of R2 and R3, and wire direct to an RCA input.

The load resistor on the transformer secondary is not specific to any particular valve or solid state output stage. Possibly does nothing in this particular config so could/should be removed.

Last edited by Little_Eddy; 20th July 2018 at 02:09 PM.
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Old 20th July 2018, 02:52 PM   #1310
316a is offline 316a  England
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Quote:
Originally Posted by Little_Eddy View Post
OK so if I wanted to have 2 inputs, I need to divert the bias voltage via the inter stage transformer with a switch. Potential scheme attached. Unsure whether the second set of switch contacts from inputs to the gate stopper is needed and seems like quite something just to get rid of C1.Attachment 692780

Perhaps just be easier investing in a better C1 if I'm that bothered about it's sonic impact.

Or probably easier, just lift one end of R2 and R3, and wire direct to an RCA input.

The load resistor on the transformer secondary is not specific to any particular valve or solid state output stage. Possibly does nothing in this particular config so could/should be removed.
Looks like a complete mess , I just enlarged the schematic and it's not readable at all now . I don't understand what you are attempting to do . Surely , your input selector goes at the input of the linestage ?

316a
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