• 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.

Recent Ad on Craig's List

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
M

MattM

Member
Joined 2005
astronomydaily.com
Ad has been pulled, but I swear I am not making this up (who could?) :)

Hi i have 8 7591 vacuum tubes that were new old stock, i tested these in a scott amplifier and worked well. I carefully removed the glass on each tube to clean both sides as all the tops had silver inside blocking view of tubes light now the tubes have no glass but may still work. asking 50.00 each.
Click to expand...
 
mark02131

mark02131

Member
Joined 2005
I'd love to see his reaction when he tries to power them up without the glass, That I actually would like to see. I am not sure what would happen. I've never powered up a tube with the seal broken.

maybe someone should tell him the glass is for protection to keep you from getting burned from the hot metal. Still all I can say is wow.
 
Salas

Salas

diyAudio Chief Moderator
Joined 2002
Paid Member
That some clueless guy could do this I find it probable, given the wide circulation of tube gear after the rebirth of interest they enjoy in audio. The real lough will be if a purchaser actually shows up. I wanna see the feedback after the purchaser will try them on some gear.:D
 
smoking-amp

smoking-amp

Member
Joined 2001
Well, lets see. Could run them outside the space station, but the electrolytics in an ampl would probably blow up out there.

Would be interesting to crack the seal just a bit, while holding the tube under water. Then put them into an amplifier.
The heaters would eventually boil the water, and ...... kaboom! (I'm not volunteering to try it though)

Hmmm, if the crack were in the top tip seal, then maybe could get a steam fountain coming out of the tubes when powered up.

Don
 
HollowState

HollowState

Member
Joined 2006
mark02131 said:
I'd love to see his reaction when he tries to power them up without the glass, That I actually would like to see. I am not sure what would happen. I've never powered up a tube with the seal broken.
Click to expand...

For indirectly heated receiving tubes that have no vacuum, not very much happens when filament power is applied. The filament lights very dimly. Pushing the voltage up will cause it to run hotter and it may begin to smoke a little and then burn out.

With larger directly heated transmitting tubes with air in them, powering the filaments causes them to immediately burn and smoke. The smoke is a pale yellowish color that coats the internal elements and the inside of the glass. Increasing filament power rapidly increases the burn and smoke leaving an awful ugly looking somewhat opaque coating on the inside which continues until the filament opens.

In both cases any plate/screen voltages applied may often cause sparking and arcing depending on the voltage level applied. I've experienced this every so often when testing both used and NOS tubes acquired from hamfests and the surplus market.
 
Tubelab_com

Tubelab_com

Member
Joined 2005
tubelab.com
That I actually would like to see.
Click to expand...

Yeah, not much happens. Sometimes the heater just instantly goes open, usually it just gets hot and does nothing. Sometimes it will make a very faint smoke.

With larger directly heated transmitting tubes with air in them, powering the filaments causes them to immediately burn and smoke.
Click to expand...

Yeah, I have seen several NOS transmitting tubes (no getter to verify vacuum) smoke internally. Usually yellow, but sometimes white.

Would be interesting to crack the seal just a bit, while holding the tube under water. Then put them into an amplifier..... Hmmm, if the crack were in the top tip seal, then maybe could get a steam fountain coming out of the tubes when powered up.
Click to expand...

Been there, done that although I had forgotten about it until you reminded me. We discovered this in the technical high school I went to where they taught a 3 year electronics program in TUBES (1968-1970). We called them DAMPER TUBES (what else?). A 9 pin power tube, or a top tip compactron works best. Hold it under water and crunch the tip with pliers. The vacuum will suck the water in, fast. Then we put it in the old tube tester and cranked the dials until the volcano erupts! Plate voltage adds to the show, and provides come crackling sound effects.

After high school I worked as the service tech in an Olson Electronics store where they had two of the drug store style DIY tube testers. On Friday night at closing time we would pop a damper tube in each tester, set them for a slow boil, then shut the store down. Saturday morning the manager would wadle in with a category 5 hangover, power up the store, and sit in his office to read the paper. He had no clue and never figured out what was going on. We had a lot of fun with him when they invented super glue!

WARNING! dont do this with any useful circuit or tube. The damper tubes will get HOT, don't touch one for a long while after it is done.
 
Tubelab_com

Tubelab_com

Member
Joined 2005
tubelab.com
Wonder what would happen if we filled the tube with that fluid mix in those chemical glow lights
Click to expand...

Can't say that I have tried that one. Glo Stix weren't invented yet when I made my last damper tube. Sounds like the recipie for a major mess though.

I did see some kids make some cool UFO's with them though. Glo Sitck inside a baloon, break the stick, fill baloon with helium, put the whole thing in a white garbage bag. Launch before it gets too dark. The blue ones look weird against a fading orange sky. Sure beats the Sterno and dry cleaners bags UFO's we made as a kid.
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom