Lafayette LA 90-b

M

maciek

Active Member
I found this small amp on moving sale,it has fried power transformer and probably can cap,the tubes are 4 el84,4 12ax7 and two rectifiers 6a4 (?),needs new transformer for sure and new caps,one of el84's had no getter at all ,could be bad and damage PT? Looks very nice built,solid cage and brass faceplate,would it be worth fixing,what transformer to use and if anyone has a schematic of this one, great thanks for any help,
 
Register to hide this ad
Hard to say if it's worth fixing. :)

That would depend on the owner, you'll probably spend $200 or so getting
it working properly if you do it yourself, and it'll be an decent little amp then.

So do you want to spend the money, can you do the work, do you have the time?
 
It will sound very good when rebuilt, if that helps you. First step would be to find a schematic and try to get the voltages you need from the power TX. Many will work just fine, you just need to know the specs, mostly the high voltage winding volts.
 
Re

Parts in question that I would need to buy are new pt and electrolytic,this is what I want to start with,I need schematic as well,where I can get right
power transformer for it?
 
Pt

I am wondering if rebuilding bad pt would be possible,what would be cost or could I do it myself,it is not that I crave that particular amp but the challenge,I finished recently restoring hk cit ii after 7 months on and off,
 
I may have a schematic - I'll check when I get home. If I have the Sams, it'll have the transformer specs...
 
Re

Thanks Tom,that would be great help,I spotted one at Radio museum,but i need to become member,might be worth it ,
 
I have the schematic, not the rest. But from the schematic, the transformer is 300-0-300V @ 160 mA, dual 6.3V windings at 3.6A each. email for a copy: tbavis(at)rochester(dot)rr(dot)com
 
Re

Tom,thanks for help,I'm going to email you for schematic,do you think that type of transformer is hard to get,does Hammond or Edcor make these?thanks again
 
What are the transformer core dimensions? I assume it's a through-chassis mount... if it's 3 3/4" x 3 1/8", Hammond has a couple of possibilities. They have a 325-0-325V horizontal mount, and a 300-0-300 that you could use by swapping end-bells. Likewise this Edcor: http://www.edcorusa.com/p/960/xpwr205_120-240

I might even have something similar in the basement...
 
Last edited:
Re

Tom thanks for your interest,I have few options for rewinding,tripod in Maine 162$,mercury 250$,heyboer 86$,also looked on Hammond you mentioned and edcor ,I'll snap a picture tonight and get dimensions, it is horizontal and has only top bell,bottom is not covered under chassis,cheers
 
Last edited by a moderator:
maciek said:
Tom thanks for your interest,I have few options for rewinding,tripod in Maine 162$,mercury 250$,heyboer 86$,also looked on Hammond you mentioned and edcor ,I'll snap a picture tonight and get dimensions, it is horizontal and has only top bell,bottom is not covered under chassis,cheers
Click to expand...

Just curious - does Heyboer have the transformer in their database, or is it cheap to rewind PTs compared to OPTs?

-D
 
Last edited by a moderator:
Re

That's how they priced it ,given specs and including my core,86 $ is pretty good,on the other hand,edcor mentioned by mr.Bavis is 71$ and is all new
made as special order,my question is what else usually goes bad with pt failure,about everything or it's not so bad?
 
maciek said:
That's how they priced it ,given specs and including my core,86 $ is pretty good,on the other hand,edcor mentioned by mr.Bavis is 71$ and is all new
made as special order,my question is what else usually goes bad with pt failure,about everything or it's not so bad?
Click to expand...

With Heyboer, you'll have original PT (if it is important for you) and Edcor, a brand new PT.

Heyboer is quite reliable and they are good people for what it is worth...
 
If a transformer dies, its the wiring inside that will have failed. The transformer other than the wiring is simply a stack of steel plates and maybe a sheet metal cover over the whole thing. Nothing there to fail really.

Also, just a simple question, but did you take an ohm meter to the transformer to verify if its got an open winding? Transformers seldom die, but when they do, often there is evidence. Commonly you'll see burned paint, and often tar or wax will have melted out of the bottom along with a generally foul smell.
 
There was blob of wax hanging and under chassis was all brown around,maybe Heyboer is better option I get to keep old lamination and get new wire,is there possibility that other components failed when pt went bad,like can capacitor or output transformers or else?what output transformers should I use in case these are bad , how do you tell from schematic specs of transformers,thanks for any help
 
can caps and quite probably the rectifier. More than likely the cap failed which took out the rectifier which may have taken out the transformer.

Have you ohmed out the transformer or put power to it to verify if its bad or not? Some look gooey and still work. I'm overly cheap, so I simply refuse to believe things are bad unless I've absolutely proven that its dead.

If you can dig up a Sam's for it, likely it will have cross-referneces for suitable replacement transformers. If you can find the specs on those, you're set. Failing that, you can usually calculate the heater winding based on how many tubes and bulbs are on it, and the HV winding voltage is usually listed somewhere on the schematic.
 
Re

What is easy way to check on transformer,chassis under all around transformer had a lot of brown residue,or maybe that was a cap,there is two rectifiers ez80 on schematic but I bought it with two 6ca4,is that right substitute for ez80?
 
You must log in or register to reply here.
Back
Top Bottom