6C33C and GM-70

[Colt45]

anyone have an opinion on these?

I'm going to get some, and cant afford to ship them both..

With 6C33C I dont need any iron.. but is 2 enough to run them into 8 ohms? also, I hear they change plate current draw after a while?

GM-70 looks cool too, but I can't afford the iron for them..
(and where the heck do i find a socket? )

[fdegrove]

Hi,

but is 2 enough to run them into 8 ohms?

You mean as an OTL amp?

Two won't be enough,you'll need at least four.

You could use two and than add the iron on the output.
This doesn't have to be of the highest quality and will give good high frequency response.

I hear they change plate current draw after a while?

They're not the best behaving tube around so you better buy more then you need.
It is a good idea to burn these in for a day or two and they take about an half hour to stabilize.

(and where the heck do i find a socket? )

The socket is a standard Jumbo 4.Not a problem,most valve vendors should carry these.

Cheers,

[fdegrove]

Since everyone is always begging for a pic:

[dhaen]

For the 6c33, if you run it hard, youll need to automatically adjust the bias constantly. It was designed as a voltage regulator.

I think you'll find the GM-70 doesn't use a Jumbo, but some wierd thing with varius diameter pins.
Most people adapt a "Septal" (6c33) socket bu drilling it. But I think the proper thing is available from 1 USA source.

Enjoy,

[fdegrove]

Hi,

Sorry,the pic got me fooled.

You mean this kind of job then?

[Colt45]

yeah, they use that odd socket.

I found a really good price on them. (lets say the tube costs less than shipping), but shipping from europe isnt too cheap, so I'd like to keep the tube count low.

(I think 6C33C is 200g, GM-70 is ~250g)

the heater is pretty heavy on both tubes.. i can deal with that though.. not sure what to do for an OPT for a GM-70..

i'll grab some 6S19P ( roughly equivalent to 1/2 6AS7/6080 ) and maybe some 6P14P too. (EL84 with slightly jacked anode dissipation [12w vs. 14w])

Ive tried 6P14P SE ultralinear before, but the iron wasnt too hot, and i still need to add a cathode by-pass sometime..

[fdegrove]

Hi,




Power triode, audio industry, hard glass envelope for high temperature operation and massive graphite anode, very low distortion. suitable for S.E. or P.P. amplifiers.

Technical features on GM-70:
Filament - DHT
Voltage (AC or DC) - 19-21 V
Current - 2.8-3.4 A
Amplification - 5.6-8.2
Capacitance
G-F - 6.5 pF
G-P - 4 pF
Maximum rating
DC plate voltage - 1650 V
Plate dissipation - 125 W


Colt45,

Does anyone know Rp of this tube?
At first glance you're going to need iron along the lines of the 845.

Ciao,

[Colt45]

I found a russian datasheet, but can't find anything for Rp.

says
resistance of <word i dont understand> = more than 20 Mohm (with a value like that they must mean pin to pin resistance or something.. no idea..)

ok.
----GM-70-----

Vf = 20±1v @ 3±0.3amps

mass = 280g at most
life = minimum 1000hrs.

------nominal ratings-----

Va = 15,000v
Ik = 800ma++ (at 180v plate and grid) -- huh?. i guess my russian is pretty bad.
Gm = 6ma/v (at Va = 600v, Ia = 160 and 260ma) -- and = or maybe? hmm.
µ = 6.7 (Va = 1.2 and 1.0kV, Ia = 125ma) -- again, huh?


---max---
Va = 1,5kV
Pa = 125w (150w for under 1 minute). (minute = minuty hehe)
reverse grid current = 40 µA


http://cityradio.narod.ru/spr/tubes/...l/gm-70_2.html
(cityradio, so its slow..)

[fdegrove]

Hello,

resistance of = more than 20 Mohm (with a value like that they must mean pin to pin resistance or something.. no idea..)

That's the insulation resistance.

This sheet is a bit easier to read perhaps:

GM70

And someone has been there before you too:



An interesting explanation of the cyrillic codes:


RUSSIAN CODING.

Ciao,

[Colt45]

ah, cool (i guess my russian wasnt that bad afterall.. compared to the english site..)

I'm too poor for that iron though.. guess I'll pass on them for now.

I'll probably try something with 6C33C. Maybe I'll have to quit smoking so i can afford more tubes..