Rectifier Failure

Powered up my rack and as the tubes came up on the VTA ST120 , the gz34 arched at the base of the glass .
Powered down and replaced with 5ar4. All came up fine but no bias ( steady .100). Without going inside the amp, I retention
all the tube pin sockets and bias was fine. Just another note on the importance of pin tension.

Which 5ar4 are you using? I used a pair of Genalex Gold Lion U77 for several weeks and thought they were nice. Put back the Webers though for no particular reason.

When I put back the WZ68's into their sockets after drilling vent holes into them I had a large spark on one of them upon power up. I always keep my fingers on the power switch when I power them on, so switched it off almost immediately. Cleaned and retentioned the sockets after that! Important to do every time a tube is pulled and replaced.

OK, well I'm excited to be finally purchasing a ST120 here in the next few months, after lurking for several years.  My Quad ESL's will thank me I'm sure.....

So how exactly does one retension the pins on the power tube and other big sockets?  All I'm familiar with is 9-pin 12Ax7 tube types, etc.

StevieRay wrote:So how exactly does one retension the pins on the power tube and other big sockets?  All I'm familiar with is 9-pin 12Ax7 tube types, etc.

In the same way.  Here's a fairly good explanation with photos...http://swartamps.com/tech/socket_retention/

With a small screw driver you are just forcing the tines of the socket pins toward the center of their respective holes.  This closes the pin socket opening and creates greater force on the tube pins when re-inserted into the socket.  More pin grip in other words.  I had to do opposite yesterday on a 6SN7 to 12AU7 socket adapter.  The pins were too tight and could not insert a 6SN7 all the way into the socket base.

Oh... and for safety make sure the amp is off and the power supply caps drained of their charge.

Any time you re-tension the sockets is a good time to give the whole smash a little squirt of De-Oxit in each pin-hole, too, especially if you've got a pet, are a smoker, or live in a dusty environment.
Let the De-Oxit dry for 5 or 10 minutes before re-lighting everything, too.

I would be careful of "DeOxit" in general - as "Mr. Natural" suggests it to be used, it is an excellent expedient. BUT! Beware of excessive use. The active ingredient(s) continue to react as long as there is a reactant available, and in some formulations it (they) are not 100% volatile. All things in moderation.

Sidebar: For several years, my wife and I worked in Saudi Arabia, I as a property manager, she as a K-8 school teacher. Of course, I maintained my hobby while there, and had the benefit of a local "electronics souk" that had all sorts of interesting stuff. In any case, the Cramolin line of products were sold there, including Cramolin Red. Some believe that Cramolin Red morphed into Caig's DeOxit when the relationship between Caig and Cramolin broke up (and a very bad break-up it was). Now, in Saudi, anything sold sealed in a can from outside the country was required to list its actual ingredients on an applied paper tag - no exceptions. On the Cramolin Can:

Propellants and other aliphatic hydrocarbons - 95%
Active Ingredient: Oleic Acid - 5%

DeOxit products were not available in the KSA, but were available in Bahrain just across the causeway. My guess is due to the labeling requirements.

Draw your own conclusions.

Peter W. wrote:I would be careful of "DeOxit" in general - as "Mr. Natural" suggests it to be used, it is an excellent expedient. BUT! Beware of excessive use. The active ingredient(s) continue to react as long as there is a reactant available, and in some formulations it (they) are not 100% volatile. All things in moderation.

Sidebar:  For several years, my wife and I worked in Saudi Arabia, I as a property manager, she as a K-8 school teacher. Of course, I maintained my hobby while there, and had the benefit of a local "electronics souk" that had all sorts of interesting stuff. In any case, the Cramolin line of products were sold there, including Cramolin Red. Some believe that Cramolin Red morphed into Caig's DeOxit when the relationship between Caig and Cramolin broke up (and a very bad break-up it was). Now, in Saudi, anything sold sealed in a can from outside the country was required to list its actual ingredients on an applied paper tag - no exceptions. On the Cramolin Can:

Propellants and other aliphatic hydrocarbons - 95%
Active Ingredient:  Oleic Acid - 5%

DeOxit products were not available in the KSA, but were available in Bahrain just across the causeway. My guess is due to the labeling requirements.

Draw your own conclusions.

In the "old days" a lot of guys just used WD-40, although how the lanolin in it messed with conductivity I wouldn't know. Maybe it doesn't.
One caveat, if you are using Deoxit: The propellant(s) are quite flammable. I had a 200-watt mogul-based lamp socket that was giving me the fan-tods, so I goosed it up real good with DeOxit then replaced and lit the bulb. With a few seconds smoke was shooting out of that puppy like shite from a goose. Didn't get to the smoke alarm in time to toss it overboard so now we had sound, too. Ranked right up there with my first red-plate experience.
For pin-cleaning, it's tough to beat Mr. Clean's "Magic Eraser" cleaning pads, which leave no residue nor catches fire.

I know there are some who do power ST120s with a tube rectifier, but unless you've got a vintage GZ34, the new ones just don't have enough current capability.
Most of them won't last couple months, if they last the first turn-on.