My ACF pre.

What people are working on at the moment
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pre65
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#16

Post by pre65 »

andrew Ivimey wrote:ummmmmmmmmmm the input phonos have a long way to go through transformer territory to get to the valves. (I imagine the outputs will be at the back of the board.) Might not this signal journey be challenged a smidge more than necessary to keep out noise and artefact?
Yes, that was (still is ?) a conundrum.

The jury is still out on the solution. :wink:
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brig001
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#17

Post by brig001 »

pre65 wrote:Well Brian, since the wife died (7 years now) my house has become more like a workshop and warehouse.
I left mine in April, and I must admit my new place keeps getting a bit like that. Like you said though, it keeps us happy, and off the streets, and out of trouble :wink:

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pre65
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#18

Post by pre65 »

I need 240v HT, and with a 10K 100W load (24ma) I get 278v, so I need to loose a bit.

A 2K resistor should do that.

Just tried a 2.2K and I've got 238V, so near enough for now.

Just got my new soldering iron in the post, a 25W Antex. The old one packed up and my 18W iron is not enough for some jobs.
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pre65
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#19

Post by pre65 »

Next test is the 6SN7 heaters.

I'm using a 9v transformer (25va) for each valve and Andrews IDH module. Thr 9v transformer gives 10v under load and with the heater voltage set to 6.3v (with the pot :) ) the heatsinks are hot-ish. I've left them on for 30 mins to stabilise and I'm happy they are not to hot.

Well done Andrew on the modules. :D

Now I need to order some resistors from HFC, so not a lot more I can do till Tuesday probably. Might look at the GK-70 layout. 8)
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pre65
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#20

Post by pre65 »

I'm sorting out the tag board wiring layout.

One thing I noticed is that on V1 the top triode is pins 1-2-3 and on V2 the top triode is pins 6-7-8.

Is there likely to be a specific reason for this ?

As both triodes in the envelope are identical does this matter ?

EDIT.

I'm doing two tag boards, one each for L & R channels.
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Cressy Snr
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#21

Post by Cressy Snr »

I can't see it making any difference.
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pre65
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#22

Post by pre65 »

Maybe it was as per Marks suggestion of using one valve for both tops and one for both bottoms to optimise the raised heaters problem ?
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Cressy Snr
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#23

Post by Cressy Snr »

pre65 wrote:Maybe it was as per Marks suggestion of using one valve for both tops and one for both bottoms to optimise the raised heaters problem ?
Yes that is probably the reason, as then you have both valve cathodes in the same envelope seeing the same heater cathode voltage. That would make a lot of sense.
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#24

Post by IslandPink »

Yes. Otherwise, I think there are only very small differences between the two triodes that might make a difference at MHz frequencies, not in the audio. I think cascode valves like 6922/6F24P have a recommended lower & upper section, but again, only significant for higher frequencies.
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pre65
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#25

Post by pre65 »

A couple of the resistors are marked as requiring " high quality types".

Would Kiwame or Tackman be considered "high quality" ?
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Greg
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#26

Post by Greg »

IMHO, YES :D
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pre65
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#27

Post by pre65 »

Greg wrote:IMHO, YES :D
That's what I thought. I've ordered Kiwame. :)
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#28

Post by IslandPink »

Don't you have a 'Nice Resistors' box where the good ones are kept , Phil ?
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pre65
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#29

Post by pre65 »

IslandPink wrote:Don't you have a 'Nice Resistors' box where the good ones are kept , Phil ?
Yep.

Box for Kiwames

Tin of power resistors (green ones)

Box for 25/50/100w resistors

Huge box of 1/4-1/2-1w resistors (several hundreds)

Box of used resistors.

:)
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David
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#30

Post by David »

IMHO, Kiwame's are very good, with no real vices. The Vishays/Charcrofts are better still but at silly prices from HFC at least. I don't know Takmans. But I'm just using the stock resistors-carbon film-and my only upgrade so far is a Mundorf input cap, I moved from my Pre3, and it sounds darn, darn good!

I look forward to your impressions!
David
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