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Old 9th October 2012, 03:34 PM   #2131
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Hi Jeffrey,

what is the advantage you are seeing in dual mono supplies for such a preamp? Even in my most elaborate preamps I have a common B+ supply. Decoupling between channels is done with separate LC filter sections with high inductance coils. Filament supplies I keep separate

Best regards

Thomas
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Old 9th October 2012, 11:39 PM   #2132
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Just seeking the last iota of seperation of channels with a common power chord. Also the rest of my system is completely dual mono and I have a fetish for bi-lateral symetry

JD

Quote:
Originally Posted by Vinylsavor View Post
Hi Jeffrey,

what is the advantage you are seeing in dual mono supplies for such a preamp? Even in my most elaborate preamps I have a common B+ supply. Decoupling between channels is done with separate LC filter sections with high inductance coils. Filament supplies I keep separate

Best regards

Thomas
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Old 14th October 2012, 08:41 AM   #2133
mogliaa is offline mogliaa  United Kingdom
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Quote:
Originally Posted by massimo View Post
Yes please!
As many have asked me for my latest schematic, here it is:
http://www.bartola.co.uk/valves/dht-...mplifier-gen2/
Still early days playing with it so may be tuning it a bit..
Ale
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Old 14th October 2012, 10:17 AM   #2134
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Thanks to share Ale.
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Old 14th October 2012, 01:30 PM   #2135
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I'm just wondering about the glow tubes here. The way I understood it you used a .056uF bypass cap rather than 1uF (edit: 0.1uf meant). Also you don't put any capacitance after the glow tubes. You have 10uF, though this is separated by a 3.3K resistor. I thought glow tubes started to misbehave when you added capacitance.

If you have this up and working then clearly it works. Maybe we haven't been reading the same theory - I just read a lot of stuff on various posts about this.

Does anyone have definitive answers to using capacitors with glow tubes?

Last edited by andyjevans; 14th October 2012 at 01:49 PM.
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Old 14th October 2012, 01:46 PM   #2136
mogliaa is offline mogliaa  United Kingdom
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Andy,
Bypass cap is 100n, not 1u. Didn't have a 56n around and it seems that the VR don't complain about that.
The additional RC is a voltage drop/ filtering stage as per Gary Pimm's.

See this:
http://www.pimmlabs.com/web/Tabor3s.gif

Perhaps an expert in VR can explain why with CCS feeding the VR additional capacitance doesn't make it to oscillate, etc....
Ale
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Old 14th October 2012, 02:36 PM   #2137
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Quote:
Originally Posted by mogliaa View Post
As many have asked me for my latest schematic, here it is:
26 DHT pre-amplifier (Gen2) | Bartola Valves
Still early days playing with it so may be tuning it a bit..
Ale


Thanks!
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Old 14th October 2012, 02:39 PM   #2138
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Because the 10uF is separated from the glow tube by a large R. Short out the 3.3k resistor and you will have problems.
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Old 14th October 2012, 02:49 PM   #2139
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Originally Posted by zigzagflux View Post
Because the 10uF is separated from the glow tube by a large R. Short out the 3.3k resistor and you will have problems.
I wasn't aware of this - it could be useful since you can adjust the final voltage more accurately. What's the minimum size resistor to give adequate separation?

Also it could help with strike voltage if the HT is restricted.
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Old 14th October 2012, 02:57 PM   #2140
10y is offline 10y  Italy
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Hi,

Wish add my newborn 26 pre to the list:

It sounds very, very well. I'm impressed for the strings and female voices.

Set up is two ux 226 (one radiotron, the other a strange green base echotron) with filament bias at 10 V, plate voltage at 150 V -around 6 mA- on two hammond 156c for channel like Andy's pre. Supply is, as Rod suggestion, a mix graetz of uf4007 and a valvo az1 mesh plate with a c-l-c-l-c (2 uF oil-15 H Hammond-50 uF polarized-15 H- 100 uF ) for a raw line of 175 V inijected on a SSHV 1.

Problem to solve in the next:


1) great microphonic effect.... all noises generated near pre will sound on speaker

2) Two box that will limit at maximum hum captation.

Thanks to all participants to this great thread. I've learned enormous knowledge reading your post.

Ciao,

Anto
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