6CG7 replacing E88CC in SE KT88 Amp. - diyAudio
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Old 16th February 2011, 09:24 AM   #1
Zekk is offline Zekk  Singapore
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Default 6CG7 replacing E88CC in SE KT88 Amp.

Guys .. I was contemplating about swopping the Tesla E88CC for a RCA 6CG7 in my SE KT88 amp. Will it sounds any better?

I'm confussed about the dissipation of 4W for 6CG7 against E88CC's 1.8W !? Is that the total or per triode?

Please advice, Sir .... thanks!

zekk
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Old 16th February 2011, 09:45 AM   #2
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They're different tubes, so there's likely to be going a change in sound. Dunno what will sound better, but at first glance, I'd be careful putting a 6CG7 in a circuit optimized for E88CC. The operating point will be rather different, and I suppose there's a risk in running the 6CG7 beyond its maximum ratings. Just speculating here though, perhaps someone who's actually tried this could give his 2cts.

BTw, any chance of posting a schematic?
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Old 16th February 2011, 11:39 AM   #3
DF96 is offline DF96  England
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They are both twin triodes, with the same pinout. Apart from that, they are very different: gm, mu, bias - just look at the data sheets. Swapping them in a circuit correctly designed for one of them could turn it from an amp into an effects box.
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Old 16th February 2011, 12:41 PM   #4
GoranB is offline GoranB  Poland
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You cant put 6cg7 instead of E88cc, anyway u should change anode and catode ressistors.
6cg7 sound more..analytic, but without soul...hard to explain, anyway its just my opinion.
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Old 16th February 2011, 08:03 PM   #5
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Quote:
Originally Posted by Zekk View Post
Guys .. I was contemplating about swopping the Tesla E88CC for a RCA 6CG7 in my SE KT88 amp. Will it sounds any better?

I'm confussed about the dissipation of 4W for 6CG7 against E88CC's 1.8W !? Is that the total or per triode?

Please advice, Sir .... thanks!

zekk
From the data sheet 4W each plate, 5.7W both plates together.

Note the difference in heater currents between E88CC and 6CG7. You will be taking an extra 1/2 amp for a pair of tubes.

Last edited by rotaspec; 16th February 2011 at 08:08 PM.
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Old 17th February 2011, 09:16 AM   #6
Zekk is offline Zekk  Singapore
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Guys ... above is my handdrawn,cut & paste circuit of the amp.
It's copied from various designers and if you found anything familiar to your's, please forgive me ... ya!?

I'm a newbie, a retired 68 yrs old structural engineer, trying to build a sweet sounding amp that'll see me thru my twilight years.

And until than, my grandsons will continue to remarks..'grandpa is with his LEGO again.. he.he.he!

Reluctantly used a 35uf oil cap after the #83 mercury rectifier to acheive a 450vdc B+. It's already into 100hrs of services, but no fireworks!

Any forecoming advices will be greatly appreciates.

Regards, Zekk
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Old 17th February 2011, 10:56 AM   #7
DF96 is offline DF96  England
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In that circuit the 6CG7 would give you less gain (around half?). It might give slightly higher distortion, as I think its anode impedance is higher. You might need to adjust the cathode resistor to get the right bias.

Assuming the circuit was designed for an ECC88, why do you want to redesign it (or, even worse, simply substitute a different valve without redesigning)?
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Old 17th February 2011, 11:10 AM   #8
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The 6CG7 is just a noval version of the 6SN7. Seems to me it will work fine, tho u will have a little less gain.
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Old 17th February 2011, 11:21 AM   #9
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Nice copy-paste work, we don't get it like that much anymore these days Does the trick nicely though.

Note that you're running the #83 beyond its limits. I'd replace the 35u with something of 8uF or smaller to stay below the 800mA or 1A maximum rating of the rectifier. I understand you're aware of this, so maybe it's a calculated risk and you have a couple of spares lying around.

Are you runnin both halves of the ECC88 in parallel? Since you stated the parameters per triode, but the schematic shows the second triode unconnected.

If you replace the ECC88 with a 6CG7 without changing anything else, it seems you'll end up with about 10mA running through it with a grid voltage of somewhere around -4V and maybe 160V on the plate. So pretty much in the same general area as the ECC88 is running, and not too far away from the load lines suggested in the GE datasheet at first glance.

So in any case, ignore my earlier remark about potentially running the 6CG7 beyond it's maximum ratings; in this circuit, you won't. I'm no judge if the operating point would be wisely chosen, because wisdom, that's one thing I don't have too much of.
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Old 18th February 2011, 02:40 AM   #10
Zekk is offline Zekk  Singapore
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Yes, it's a calculated risk by using 35uf instead of 4uf regularly used by the some of the gurus on this forum. But then, the B+ will drops to 385v unless, I resort to using the original 5AR4, which is very good.

Half a Tesla E88CC (not ECC88) is used per channel.

6NIP is the original driver. Then I swopped to a 6DJ8, and then a 5687 and finally a E88CC. Off-course, needs to re-adjust the parameters to that sweet spot.

We're all here because of the passion in us to explore the magic tonality of vacuum tubes.

Greatly appreciates all the responses.

Cheers!
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