833A (GU-48) Amp

What people are working on at the moment
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pre65
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#1081

Post by pre65 »

IslandPink wrote:Interesting ... sounds like a worthwhile exercise though . What voltage are you aiming for with the GK-71's ?
It would be good to hear what they can do at 700 or 800V .
Probably more like 600v in choke input. Going to stay with triode mode at first as it was well received at Owston. :D
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#1082

Post by pre65 »

The last bits of hardware are now here, the 193Q chokes.

That's what I call a choke. :lol:

Can't start yet cos I'm decorating the man cave, stripping off wallpaper at the moment. This job should have been done in 1991, but other things always seemed to get priority. :wink:
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#1083

Post by pre65 »

With my amps one of the filament (cathode) terminals is grounded (negative).

Instead, could I form a centre tap with two resistors and ground the join, or am I talking bollocks ? :lol:
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#1084

Post by Alex Kitic »

pre65 wrote:With my amps one of the filament (cathode) terminals is grounded (negative).

Instead, could I form a centre tap with two resistors and ground the join, or am I talking bollocks ? :lol:
You should by all means do that, regardless on the type of heating arrangement you are using. The two resistors should be around 47 ohm each, well matched pairs on each channel.

This will form a "virtual cathode arrangement" that you can ground, if you are using the amp with fixed bias.

If you have tried to use 50Hz AC heating with your current arrangement (one terminal grounded) you must have had "LOADS" of hum. The "virtual cathode arrangement" is beneficial even with DC...
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#1085

Post by pre65 »

I'm costing up the filament supplies using parallel pairs of Rod Coleman regulators. I've had a quote from Rod, and now I need to price up the raw DC supply.

The "midlife crisis" amp on DIY audio used Rods modules, and his raw supply uses a 20v transformer. Antek do a 500va toroid with dual 20v secs so a pair of those should be man enough with a bit in reserve. :wink:
Last edited by pre65 on Wed Jul 30, 2014 10:50 am, edited 1 time in total.
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#1086

Post by Cressy Snr »

Go Phil!
Up and at 'em! :)

Looking forward to seeing this one develop.
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#1087

Post by Alex Kitic »

I must stop spamming all relevant topics with my advice and comments, so this is written instead of some advice or comment.
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#1088

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Alex Kitic wrote:I must stop spamming all relevant topics with my advice and comments, so this is written instead of some advice or comment.
Alex, I have read and digested all your efforts on HF AC heating, but I choose to go in a different direction. Does that make me "wrong" or you "stupid" ?

I think not.

The thing with information is you can only make it available, or the old saying "you can lead a horse to water , but you can't make it drink". :wink:

So grow up a bit, and don't sulk, or take offence if people use their own brains to do things in a different manner. If you carry on like this you risk denigrating all the good things you have informed us about. :(
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#1089

Post by Paul Barker »

I can't say I have had a problem with HF AC heating in the past. But some people recon they did.

I rather fancy a pure signwave HF AC heater supply to make absolutely sure we aren't missing a trick. Could more easily be done on low powered valve like 6b4g, or perhaps 10y. That would be nice to try it on right?

Build one of Andrews modules to power a 10y and try a pure sign wave HF ac heater supply. AND try a cheap lighting transformer.

Someone has to do it. Can't just keep arguing with Alex, have to give his present direction an airing. He is after all the only one on here actually hearing what he is promoting.

I don't believe that it is healthy to dismiss a person with the aural experience until you have the same experience.

I know some of us have had the experience in the past. But time has passed. I wouldn't argue with him until I had revisited the technique.

Most I would say is. "Glad that works for you Alex, it is one of many ways to heat a valve. Must get round to trying it one of these days."

Like Nick I have things to worry about that mean going hell for leather building every whim that enters my mind isn't practical for the forseable future. So I won't be the one practically proving Alex right or wrong.

But you haven't seen me dismissing him or swatting him off like he was an anoying fly have you?
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#1090

Post by Alex Kitic »

Thank you Paul.

That is exactly what I am trying to do: find people who are willing to try and thus be in the position to judge for themselves. Thus when I see that someone who seems a likely candidate, I try to persuade him into doing it. No luck so far.

Paul has obviously got a lot of other stuff going on, but there are others on the verge of doing some modifications or applying something new to their projects. It's a cheap approach to heating, and it's footprint is also rather small, therefore easy to include in existing chassis (if any).

Never mind: in time people will try and probably they will be just as happy about the result as I am. After a few years, maybe this will be recognized as one of the better and simpler ways to heat directly (and indirectly) heated tubes.
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#1091

Post by pre65 »

I heard a pair of these tonight. :)

Image

interstage-transformer 833-based 140kg Reference monos outputting 150 watts in class A single-ended triode mode with a 6C45 driving a 300B driving the 833
Trafomatic builds amps of any persuasion particularly since they specialize in custom commissions of late. TruLife does single-ended no-feedback direct-heated triode amps exclusively. What's more, the Greeks categorically reject signal-path capacitors to favor ultra-wide bandwidth interstage transformers of the 2MHz 0.1dB sort.
Circuit topology: Class A, Zero Feedback
Output Power: 150W
Input sensitivity: 1,2V
Dimensions: 55cm(W)x35cm(H)x75cm(D)
Weight: 120kg
AC Power Consumption: 850W
Tubes complement: 1x833A, 1x300B, 1x6C45, 1x5U4G
Inputs: One single ended RCA
Input Impedance: 100kOhm
Transformers (per channel): Two Power Transformers
Two Interstage Transformers
One Output Transformer
Six Chokes

Rather nice. :wink:
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#1092

Post by Alex Kitic »

pre65 wrote: interstage-transformer 833-based 140kg Reference monos outputting 150 watts in class A single-ended triode mode with a 6C45 driving a 300B driving the 833...

Trafomatic builds amps of any persuasion particularly since they specialize in custom commissions of late. TruLife does single-ended no-feedback direct-heated triode amps exclusively. What's more, the Greeks categorically reject signal-path capacitors to favor ultra-wide bandwidth interstage transformers of the 2MHz 0.1dB sort.
Rather nice. :wink:
1) Trafomatic is not a Greek company.

2) Maybe TruLife is a Greek company?

3) Is it 140 or 120 kg... please decide ;)

4) Never heard of such interstage transformers?! At least I don't think that is possible with any DC in the primary... and if there is no DC, there must be a cap in the path.

5) A cap should not hinder your high frequency bandwidth, unless used in a filtering role.

6) Besides the shiny cheapy looks of it, nice... but not floored?

I guess you met with Baron Munchausen?
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#1093

Post by jack »

Alex Kitic wrote:2) Maybe TruLife is a Greek company?
It is - founded in Athens.

They're very Greek indeed - the MD is Velissarios Georgiadis - I'm pretty sure that's not an Irish name...

A pair was on eBay recently for GBP 27K. Didn't sell. Supposedly they retail at USD 250K - the auction stated "HAPPY TO SWAP FOR A CAR OR HOUSE IN FRANCE"

Oh, and it's 120kg - http://www.trulifeaudio.com/products/it ... rence.html
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#1094

Post by pre65 »

Spurred on by what I heard last night, I've got one of the 833 monoblocks on the bench.

The old mains transformer and associated PSU bits and pieces have been removed and the new transformers and chokes are being trial fitted to see if there is room on the trolley.

More news later. :wink:
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#1095

Post by jack »

pre65 wrote:... and the new transformers and chokes are being trial fitted to see if there is room on the trolley...
More importantly, is the trolley man enough to take the strain :)
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