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Old 11th December 2011, 06:29 PM   #1191
CSlee is offline CSlee  United Kingdom
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I guess I figured that the sudden uneveness of the plate voltages was related to the vast drop in output level.

What are potential causes of an output signal suddenly being very weak, when was fine before? LED bias is pulling 80mA, HT is fine, soldered joints 'seem' fine.
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Old 11th December 2011, 06:45 PM   #1192
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Quote:
But signal at plates SHOULD be balanced if you mesure WITHOUT global NFB.
The NFB could introduce some unbalance in an attempt to compensate for output tubes unbalance ! That's life.
Yvesm,

My amp has no GNF. Is the balanced signal the result of correctly setting the pot under quiescent conditions? Could you give us instruction on how to balance the " signal" at the plates?

Brgds Bill
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Old 11th December 2011, 06:49 PM   #1193
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Quote:
Originally Posted by Yvesm View Post
With the ccs in the cathodes, the quiescent plate voltages of the LTP WON'T be equal because of tube dispersions, this is NORMAL, do not try to balance them.

But signal at plates SHOULD be balanced if you mesure WITHOUT global NFB.
The NFB could introduce some unbalance in an attempt to compensate for output tubes unbalance ! That's life.

Anyway, a perfect balance will only reduce the amount of produced even harmonics and this may not be a good idea sonically speaking

Yves.

Thanks again Yves. I do not use NFB for the time being. Only a 18k shunt feedback. I will do some more measurements tomorrow.
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Old 11th December 2011, 07:57 PM   #1194
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leave them as I tested outside of the amp for 38mA? Right now they are around
9V.
Just leave them I would say. I just balanced the plates of the input tube with the potmeter.
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Old 11th December 2011, 08:24 PM   #1195
vgeorge is online now vgeorge  Greece
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Thanks Bas, I did that already.
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Old 12th December 2011, 05:09 PM   #1196
CSlee is offline CSlee  United Kingdom
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Took it into work today to get it on a scope. Found the fault pretty quickly when I started thinking sensibly. Turns out it was a faulty input switch. My boss said that sometimes the contact on silver switches goes bad if less than 50mA is passing through it. News to me.

Until the next drama
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Old 12th December 2011, 06:04 PM   #1197
CSlee is offline CSlee  United Kingdom
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Some pics.

A friend is building a nice wooden case for it, so I am looking forward to that, but not looking forward to the extra weight!

I call it Soho because of the tall buildings and the sleezy RLD

Thanks to all for your help

Charlie
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Old 12th December 2011, 06:17 PM   #1198
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A quality build, would love those OT's.....................
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Old 12th December 2011, 06:23 PM   #1199
CSlee is offline CSlee  United Kingdom
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Thanks Bill. It's only my 3rd amp, still learning a lot but Im glad the layout worked... it did get a bit tight!

As for the James OPT, they worked out to be about 95 each including delivery and the huge import tax. So only a few quid more than some Hammonds. Had the PT and choke wound from majestic, they are huge!

I am now completely broke, and therefore ready for the next project
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Old 22nd December 2011, 03:59 PM   #1200
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Originally Posted by gingertube View Post

... For a new preamp Allen Wright sent me his latest schematics for the SPV2 about 2 months before he died. They were provided on a "Comercial in Confidence" for my personal use ONLY basis, so please, no-one ask to have them posted because I won't.

Cheers,
Ian
Ian,

Although a bit off-topic, I will pose my question here, since it has to do with the subject appeared in this thread:

Does the SVP2 have great differences in relation to the published SVP?

I have already built the FVP preamp (phono + line) a long time ago (1999), before late Allen Wright decided that he would no longer use a MOSFET anywhere in the audio signal. I have been thinking of modifying it to a SVP.

Thanks.
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