CV2799

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Dave the bass
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#106

Post by Dave the bass »

simon wrote:Mmm............ cork that has plugged his youthful conduit for so long...
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#107

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Why thank you sirs :-)
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pre65
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#108

Post by pre65 »

Talking with Mike H at Owston about this amp, he suggested giving it a bit of cathode bias as well as the positive grid bias.

Trouble is I've forgotten what size resistor he suggested. :oops:

Anyway, I've stuck a 62R resistor twixt cathode and ground, and it's given me a bit more gain. (or so it seems :wink: )

It still sounds wonderful, playing some Siri Svale Band at the moment to make sure.

Perhaps Mike can remind me of the resistor value when he gets home ?
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#109

Post by ed »

pre65 wrote:
It still sounds wonderful, playing some Siri Svale Band at the moment to make sure.
just my two penneth but that's not exactly what I would use for deciding whether kit sounds ok. It's probably one of the best produced ensembles in my entire record collection....she makes anything sound good.

:)
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#110

Post by pre65 »

ed wrote:
pre65 wrote:
It still sounds wonderful, playing some Siri Svale Band at the moment to make sure.
just my two penneth but that's not exactly what I would use for deciding whether kit sounds ok. It's probably one of the best produced ensembles in my entire record collection....she makes anything sound good.

:)
Fair point Ed. Can't understand why not many other peeps rave about her.

Next up will be "young persons guide to the orchestra".
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#111

Post by Mike H »

Paul Barker wrote:the trouble is Phil we are ignorant without the curves. If that works for you at the moment do that.

You are pioneer for all of us.
Found this:

CV2799 is military version of QQV03-20 which just another version of QQV03-20A

http://www.r-type.org/pdfs/qqv03-20a.pdf


I've forgotten how you're doing this, it is triode wired and is it both sections paralleled together?
 
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#112

Post by pre65 »

It's parallel single ended pentode.

I'll try and draw out the circuit so it can be seen by all you experts. :)
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#113

Post by Mike H »

That would help greatly 'cause at the mo I can't envisage it, too many options
 
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#114

Post by Mike H »

According to its datasheet it's a beam pentode. (Even though it sez 'tetrode')
 
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#115

Post by pre65 »

Try this for size. I could bypass the input valve cathode resistor with a cap to gain gain. What size might be worth a try ?

Any observations, or sightings of cock ups welcome.


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#116

Post by pre65 »

Actually, the 10H choke is only rated at 90ma so it needs rewiring so it's in the driver valve HT line.
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#117

Post by Mike H »

Erm ~ I see no supply cap for the HT between the 10H choke and the OPT? :?:

As a temporary measure at least yes V1 cathode could be bypassed to ground, say 220uF?
 
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#118

Post by Mike H »

Right so according to its datasheet, for example:

EDIT: using graph on page 25

Va = 400V
Vg2 = 200V
Vg1 = -8V (-ish)
Ia = 2 x 50 mA (100 mA)
Ig2 = 2 x 4 mA (8 mA)

This is a transmitter valve so probably needs a grid stopper.

HTH
 
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#119

Post by pre65 »

Been doing a bit of reorganising.

The 1K on the HT was decoupled (but not on drawing :( ), I've rewired the choke into the driver valve circuit only, and replaced the G2 resistor (20K) and fed it from HT. Also put a 220uf cap on driver valve cathode.

First listen shows too much bass, and after a while some hardness up top.

I've gone back to the G2 resistor as it was, now 47K and to anode, seems to have got rid of the harshness. :)

Still got the excess bass, might try a 100uf cap in place of the 220uf soon,or just remove it perhaps.

Work in progress. :lol: Thanks for the Advice Mike. :)
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#120

Post by Mike H »

Ye-es, could be this is a 'hard' valve. By connecting grid resistor to anode it's sort of triode connected, but lowers the Voltage on the screen.

You might try a couple more things, put a grid stopper on the CV2799 and some resistor across the IT secondary to load it a bit, probs could flatten the freq. response more. :?:

Currently scratching my head over 6AC7 pentode. Got these working well I thought some years ago as a driver, then found must have a low impedance source (at the time, my sig gen) else all goes pear-shaped.
 
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