• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Buying guideline for 6c33c

Status
Not open for further replies.
Jump to Latest
#4
albertli said:
Guys,

I lately brought 8 6c33c from Russia n been waiting 3 months for the tubes. End up I have 3 dead tubes n the others are with the range -80 to 90v @200mA. Are they all bad tubes?

Albert
Click to expand...


got mine from moscow after 8 months....😱
8 pcs....don't just give up on those dead tubes,
scrape off the pins, mine tested as open filaments at first..
worked fine after i worked on those pins...😉
 
#6
AJT said:
got mine from moscow after 8 months....😱
8 pcs....don't just give up on those dead tubes,
scrape off the pins, mine tested as open filaments at first..
worked fine after i worked on those pins...😉
Click to expand...
New 6C33 tubes had the pins protetec by a wax layer, in military use they dont remove the wax at all.
For hi fi use the pins and socket must be clean of course.
 
Last edited:
#7
i tried the pin cleaning after the tubes tested open filaments...
the pins looked normal at first look until you test them..
had the same experience with the GU29 someone gave me saying it didn't work...
not wanting to just give up, i cleaned the pins using a fine grit sandpaper...
 
#8
albertli said:
Thanks for the head up, I have them clean with steel wool before test. I don't know all that -90v @200mA tubes are safe to use.
Click to expand...

Not sure I follow you on this, if they are consistent and don't drift once warm they should be ok. Consider burn in before use, and prior to serious evaluation of their quality. Download the data sheet and compare to the curves, bearing in mind that the transconductance is pretty high/steep slope so significant variations are possible.
 
#10
When I was running amps with 6C33 I also ran them at a max plate dissipation of 40W and plate voltage of no more than 150V. (This was an ill-fated OTL)

Tubes were burned in filaments only for 24 hours (perhaps less, no longer remember) and then run for a number of days at 120V and 200mA.. They tended to be pretty stable after that - provided they survived.

I learned to do this after having a number of new tubes arc over almost immediately during warm up - this never happened with seasoned tubes.
 
#11
Kevin,
I did burn the filaments for almost a day before test. 3 of them sitting at more than 650mA -95v. I have no chance to tune them down with my -100 supply. 2 have dim filaments n I could feel they just luke warm. End up I only have one tube -80v 200mA, and two -88v 200mA. What a good experience but it didn't happen to me before.
Albert
 
#12
Dim filaments is an indication of corrosion on the filament pins, give them a good clean and see if that doesn't help.

I bought a couple of dozen and had quite a large fallout (five or six) although it is so long ago I no longer remember the exact number.

I'd lower the plate voltage, that will allow you to get them under control with the -100V supply you have on hand.
 
#13
kevinkr said:
Dim filaments is an indication of corrosion on the filament pins, give them a good clean and see if that doesn't help.

Will try cleaning them one more time n see.

I bought a couple of dozen and had quite a large fallout (five or six) although it is so long ago I no longer remember the exact number.

I'd lower the plate voltage, that will allow you to get them under control with the -100V supply you have on hand.
Click to expand...

Good hint, thanks
 
#14
kevinkr said:
Dim filaments is an indication of corrosion on the filament pins, give them a good clean and see if that doesn't help.

Will try cleaning them one more time n see.

I bought a couple of dozen and had quite a large fallout (five or six) although it is so long ago I no longer remember the exact number.

I'd lower the plate voltage, that will allow you to get them under control with the -100V supply you have on hand.
Click to expand...

Good hint, thanks
 
#15
albertli said:
Kevin,
I did burn the filaments for almost a day before test. 3 of them sitting at more than 650mA -95v. I have no chance to tune them down with my -100 supply. 2 have dim filaments n I could feel they just luke warm. End up I only have one tube -80v 200mA, and two -88v 200mA. What a good experience but it didn't happen to me before.
Albert
Click to expand...

Burn in your filements without any high voltage on the anode can destroy a tube.
 
#16
esltransformer said:
Burn in your filements without any high voltage on the anode can destroy a tube.
Click to expand...

Yes, cathode interface - for some reason this is the recommendation I received from a number of people using these tubes, and it seemed to help quite a lot, this was then followed by some period of time running at relatively modest dissipation levels to stabilize emission, etc. As always YMMV.
 
#18
kevinkr said:
Yes, cathode interface - for some reason this is the recommendation I received from a number of people using these tubes, and it seemed to help quite a lot, this was then followed by some period of time running at relatively modest dissipation levels to stabilize emission, etc. As always YMMV.
Click to expand...

It' s a bad idea to do this, your filment will be poisened and life will be much shorter.
I used 6c33 for almost 15 y with no faillures* at 200V/ 250mA. I did use each tube for about 1000 hours and then take a new one and saved the old for experiments.

* except mistakes i did myself
 
Status
Not open for further replies.
Top Bottom