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Old 21st September 2003, 09:01 PM   #11
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Hi,

Quote:
I wonder if I should start thinking abou the next driver stage just one day after I built this one though
LOL.

By the time you have your set of tubes you may have a more precise idea of what is lacking and why...

Having a set of 6C45s around is never a bad thing.

Caveat one, I hear dispersion between tubes can be rather wild so have them matched by the dealer.

Caveat two, these tend to HF oscillation so use stopper resistors to tame it.

Cheers,
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Old 21st September 2003, 09:15 PM   #12
Sjef is offline Sjef  Netherlands
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Yes the 6C45 is a noval tube. It has cirillic signs in his name so you can search with 6C45, 6C45P, 6C45PE or 6C45Pi, they are all the same tube. They are made by Sovtek and I believe also some other manufactires. I only know the Sovtek. They like to be driven at 150 to 180 Volts with 15 to 35 mA through them so they could be used in your setup as well.

It's hard to say anything about the sound differences I'm using the 6C45 in my preamp and the ECC99 in my poweramp. I'm using them instead of the 417A/5842 wich was in there before. I didn't use them in my power amp to avoight the multiplying of two same kinds of flavour.

The 6C45 sound very much the same as the 417A but has got a slightly lighter and more transparant midrange and most important they are much much much easier to get, every Sovtek dealer can deliver them.

look also at previous topics in the forum about the 6C45.

Since you are using one ECC99 per channel you could also try paralelling the both halves to get more gain and then deside if the added gain helps out.
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Old 21st September 2003, 10:58 PM   #13
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Quote:
Caveat two, these tend to HF oscillation so use stopper resistors to tame it.
That subject came up in every discussion I read about this tube. One resistor close to each grid pin, then join the other ends together and connect to the input RCA.

What about the ECC99 - would that need grid stoppers too? How can I tell if it's oscillating? I can see some RF hash on my signal (both at the driver's plate and at the OPT secondaries), but it's always been that way, and my scope probes aren't anything special so I don't know if I should trust anything I see at such high frequencies anyway.

Quote:
Since you are using one ECC99 per channel you could also try paralelling the both halves to get more gain and then deside if the added gain helps out.
I thought about that, but that'll double the current requirements, and it'll also double the Miller capacitance of the input, which will probably make it a tough load for my passive linestage to drive.
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Old 22nd September 2003, 12:26 AM   #14
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Hi,

Quote:
That subject came up in every discussion I read about this tube. One resistor close to each grid pin, then join the other ends together and connect to the input RCA.
When trying to combat RF oscillations it is of the utmost importance to mount the resistor as close to the pin of the tube as possible otherwise the effect of the stopper will be lost.

Too high a value and you'll impart the sound of that resistor throughout the amp often making for a dulled, lifeless sound.

Too small it'll have little or no effect.

Quote:
What about the ECC99 - would that need grid stoppers too? How can I tell if it's oscillating? I can see some RF hash on my signal (both at the driver's plate and at the OPT secondaries), but it's always been that way, and my scope probes aren't anything special so I don't know if I should trust anything I see at such high frequencies anyway.
The ECC99 shouldn't need any but when in doubt a O-scope comes in handy.
You need to isolate the stage to be able the pinpoint the problem to that particular tube.
What you saw so far could well come from your source.

Quote:
I thought about that, but that'll double the current requirements, and it'll also double the Miller capacitance of the input, which will probably make it a tough load for my passive linestage to drive.
As you may know there's no free lunch in electronics, it's always a give and take situation.

Since the Miller capacitance is multiplied by the amplification factor of that stage you can well imagine it's more of a problem with higher tubes than with lower ones.

There are ways to compensate for this however by using nulling caps but in all honesty I'll need to do some reading up on that topic...
It's been ages I used that but it can be effectively applied.

Cheers,
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Old 22nd September 2003, 12:40 AM   #15
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Quote:
You need to isolate the stage to be able the pinpoint the problem to that particular tube.
What you saw so far could well come fom your source.
Well, I did short the input to ground with a clip lead, but the interconnect to the linestage was still connected. On a side note, I did notice the level of hash go down significantly when I changed the chassis ground to connect close to the input tubes, instead of in the back near the PS like I had before.
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