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Are CRT trannys OK?


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5/26/2000 9:19 PM
Patrick Are CRT trannys OK?
A local surplus outlet has several pallets full of old CRTs for cheap. They have power transformers that look to be in the 50W range. I suspect these are fairly high voltage secondaries of little use for guitar amps. There also don't appear to be any tubes other than the CRT. Anyone know what the filament voltage is on a CRT? Anyone have any idea if these might be of use?
 
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5/28/2000 2:40 PM
Graywater

Patrick:  
 
Depending on the age these have a B supply of 800v-3kV or so - voltages went up over time as size increased, etc, you probably have an A supply of 1.5-6.3 VAC - again depends on age. You mentioned no other tubes. If so you have a SS rectifire which means your tranny is probably 6.3/1,500 and up. If there's a rectifier tube then you've also got a winding of 2v - 5VAC for it. Generally the trannies are only good for repairing other scopes.  
 
GW
 
5/28/2000 5:14 PM
Patrick
Thanks GW. I suspected as much. They don't allow any testing of this stuff, they are sold "as is" so I'll pass on them.
 
5/29/2000 6:19 AM
Steve Ahola

GW:  
 
    Rumor has it that the PT's for the old B&W teevee's could often be used for guitar amps. To determine the current that each tap could handle you would look at the ratings for each of the tubes on that tap... Or so the rumor goes.  
 
Steve Ahola  
 
P.S. When Patrick mentioned CRT trannies I was thinking of computer monitors... ;)
 
5/29/2000 12:59 PM
Graywater

Hey Steve,  
 
Tis true - especially the older, pre-solid state rectifier sets - some of these even used two B supplies with two HT windings and separate rectifiers (usually 5U4s) - these are getting pretty scarce nowdays and you're probably aware that there are now "vintage" TV restorers and "vintage" is creeping slowly up into the 1960s (square plywood box with real or fake walnut veneer - what I cut my teeth on).  
 
As to the monitors - since Patrick stated "CRT" I assumed these were either surplus military or lab units - just a cathode ray tube and its associated power supply and access to the deflection plates and perhaps the cathode - these were used observe all sorts of stuff - modulation monitors, etc. - before DMMs were widely available this was you're most sensitive millivoltmeter - I used these to set the bias on transistor amps in the 70s.  
 
GW
 
5/29/2000 1:28 PM
Patrick
Steve/GW- Yes, what I was looking at appeared to be old lab type monitors. All open framed. I forgot to mention you aren't allowed to test this stuff on site, so you are guessing at what you are getting. This works great if you know what you are looking at. It is the surplus outlet for Az State Univ. Last year I picked up several small "modules" that appeared to be part of some old medical monitoring equipment. I paid about $3 each for them and got a bunch of Amperex and Mullard 12AX7s and several small "champ" sized power trannies. It is often in the timing :). - Pat
 

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