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Old 26th April 2011, 09:20 PM   #141
Salas is offline Salas  Greece
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It worked better for hum with the primary floating for ''balanced'' transfer, but it worked both ways.
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Old 26th April 2011, 09:30 PM   #142
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Its no big deal to try it both ways.......


I will take some pics soon.

Fran
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Old 27th April 2011, 06:32 PM   #143
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I promised a few pics:

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The layout might seem a little odd - the reason for the valves being in the centre is because I had the case already (with a 5th hole for a rectifier valve). The other thing is that the input transformers will most likely move from their current location to over the right hand side to place them far away as possible from the input AC wiring. I didn't read/think of putting the rectifiers and first cap in the transformer box.... so seeing as I've built each module I will leave it as it is unless there is a problem.

Both boxes are earthed, and I have a wire for signal ground from the phono box to the transformer box back to earth with back to back diodes//cap//15R power resistor. I need to organise a TT ground point on the phono box too....


Fran
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Old 27th April 2011, 07:00 PM   #144
Salas is offline Salas  Greece
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Looks fine, but try not to bring anything AC PSU feed inside the signal box. Unless you will get lucky.
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Old 1st May 2011, 05:28 AM   #145
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Hi all,

I'm back from my holiday on which I indulged in days of live bluesy, rootsy music... lovely. ZZ Top was probably my highlight.

Woodturner, great to see significant progress! I'm yet to order many of the parts for my attempt.

I have a simple question as a new-comer to valve work, that I was not able to answer clearly through research. It relates to the valve sections and the relative envelopes that each one resides in. As far as my knowledge takes me, it is customary to use one valve envelope for two valve elements in a given channel. In the case of the Itch, the two valves in the input section (2x 6N2PEV) would reside in the one bottle. However, I think that this is not correct for the Itch as the voltage potential between the two valve sections is not safe to have within the one envelope... hence why the heater voltages must be referenced differently. Assuming this is the case, then the "upper tier" 6N2PEV of each L & R channels would be in one physical valve, as would the "lower tier" input valves of each channel... similarly for the upper and lower output valves.

Could someone please clarify which valve sections in the schematic can share the one valve bottle? If what I have described above is correct, can this influence crosstalk performance, or does the dividing grid in the 6N2PEV take care of this?

Regards,
Tani.

Last edited by taniknight; 1st May 2011 at 05:36 AM.
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Old 1st May 2011, 06:38 AM   #146
Salas is offline Salas  Greece
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This is the arrangement. The dividing screens will be grounded.
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File Type: jpg HliftItch.jpg (118.8 KB, 470 views)
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Old 1st May 2011, 08:26 AM   #147
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Thanks Salas,

That's what I thought. I'm thinking about layout at this stage so I figured I'd clear it up now as it could make a difference as to where I decide to place the inputs/outputs and so on.

Cheers.
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Old 1st May 2011, 08:15 PM   #148
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I have most of the circuit wiring done now, I'm waiting on the K42Y coupling caps to arrive. I do have some other GE 0.68uF caps here that I know sound pretty good, so I might push them into service.

The RIAA caps are some nice matched mica/k42Y types from Russia via some Greek generosity (the mica measured 15.5nF, so a shade high). The output caps are some MKP types I had from a long time ago.

The pic is probably the worst quality one ever (phone camera) but give the idea at least.


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Fran
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Old 1st May 2011, 09:35 PM   #149
Salas is offline Salas  Greece
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+0.5nF on the Riaa HF cap can verge it to dull mind you. But wait to listen to it first because the cap meter might be happy. The interstage must not be bigger than 0.047u-0.1u also. The output cap lower limit depends on what load it has to couple, naturally. Thumbs up for the quick progress.
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Old 1st May 2011, 09:42 PM   #150
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George also sent me K42Y 15nf - but recommended the mica type to try first. Happy to do that!

Tracking shows that the K42Y caps are in Russian customs. I'll search my parts drawer for something!!

Fran
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