CV2799

If they glow, this is the place to be
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pre65
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#1 CV2799

Post by pre65 »

I got some CV2799 valves ages ago by mistake thinking they were substitutes for 832a.

Now, could they be used for A2 experiments similar to what I am trying with 1626 ?

Where do I start ? :?

http://www.tubecollector.org/cv2799.htm

200-230v HT would be nice, just need a rough idea of how to calculate a cathode resistor then I can experiment. :)

I'd double up the anodes and grid 1 and triode connect for simplicity and possibly (shared) cathode current around 50ma.

OR could I just ground the cathode ? :?
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#2

Post by pre65 »

The madness continues.:wink:

I've gutted the old 300b chassis, and it now sports a pair of B9a sockets to suit the CV2799.

The chassis is rigged up to feed from the 450v dual mono PSU, so that is one less job to sort out.

I will draw out some sort of plan before too long. :)

Any help with how to bias the cathode, or pointers to info which would guide me would be appreciated.

IDEA ? If I wanted to get (for example) 50ma would it be easier to have a 50ma CCS on the cathode ?
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#3

Post by Paul Barker »

pre65 wrote:
IDEA ? If I wanted to get (for example) 50ma would it be easier to have a 50ma CCS on the cathode ?
that's one way to skin this particular cat, which has often been recommended but I haven't tried it.
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#4

Post by pre65 »

Paul Barker wrote:
pre65 wrote:
IDEA ? If I wanted to get (for example) 50ma would it be easier to have a 50ma CCS on the cathode ?
that's one way to skin this particular cat, which has often been recommended but I haven't tried it.
It works very well on the push pull 832a amp. :D

There is a voltage and current limit on G2, so I'm allowing for that when connecting up in triode mode.
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#5

Post by pre65 »

After a morning of cobblering things together, I switch on and get no sound. :?

So, after a lot of checking and head scratching, I decide to ground the CV2799 grid.

Now it works. :shock:

It's only been on a few moments, but I'm impressed

A) because it actually works. :D

B) it sounds very full and dynamic. :wink:

More listening me thinks.

PS Who needs 300b ? :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol: :lol:

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#6

Post by pre65 »

Must say I'm astounded how good this lash up sounds. :D

If I can get this good without really knowing what I'm doing just imagine how good things could be if I was edumucated like wot some of you others are. :lol:
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#7

Post by Paul Barker »

You are a star Phil.

So is that the HT supply at the front, the preamp at the back and the output stage between the two?
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#8

Post by pre65 »

Dual mono choke input HT PSU at the front, the TDA2050 driving stage at the back and the CV2799 bit in the middle. Now it works I will integrate the middle and back bits somehow.

I resistored the HT down a bit cos it was about 470v and I was looking for about 440v.

The only bits I had to buy were 4 Kiwames from HFC, and I ended up not using them. :wink:

I need a hum pot on the AC heaters but I have the pots to hand. :)
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#9

Post by Paul Barker »

pre65 wrote: I resistored the HT down a bit cos it was about 470v and I was looking for about 440v.
As a project to learn from you could instead, starting on one monoblock build a shunt reg to get the voltage where you want it.
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#10

Post by pre65 »

pre65 wrote:
I need a hum pot on the AC heaters but I have the pots to hand. :)
Hum pot has made no difference. :?

The wires are a bit long in places, I'll wait till it's been tidied up before I worry too much.

Regulated power supply. :shock: :lol:

I need a member of my listening panel to hear it as is first to make sure it's not just my euphoria. :wink:
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#11

Post by pre65 »

It's still amazing me with the way it sounds.

And it's so simple really. :)

The bass is particularly good, firm and tuneful. Best bass of any amp I've ever heard with my speakers. :D
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#12

Post by Paul Barker »

that is a worthy recommendation. I am pleased your amp chip didn't work out as good.
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#13

Post by pre65 »

Paul Barker wrote:that is a worthy recommendation. I am pleased your amp chip didn't work out as good.
The amp chip is still driving the CV2799. :wink:
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#14

Post by Paul Barker »

Shock horror!

It must be therefore that the amp chip you chose isn't capable of driving far into A2 but is fine with this load.

So now you tell me that effectively a hybrid amp is your best to date?

somebody help me my world is sinking beneath my feat.

Oh well nothing else for it, like smokers pooh pooh the evidence that smoking is bad for you, I will regress back into my own little world of valves alone, and pooh pooh this evidence.

It is not good for my sanity to accept this paradigm shift. I will pretend I never heard this.
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#15

Post by Mike H »

The amp chip -> A2 worked fine, just wouldn't do treble at the "away match" (tried at someone else's house) :D
 
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