PCL86 Tube Pre-Amp for guitar. Any Idea?

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#22
PT rattling: probably some of the laminations or windings became loose.

If you don't mind getting messy, there's a way to fix it: You could put it in a suitable box, like an old tuna can, and fill it with epoxy resin or something similar. Then while the epoxy is curing, put everything inside a stout plastic bag, and make a vacuum using a pump. This will cause all the air being sucked out (and replaced by epoxy) from between the windings and laminations. Most likely then the buzzing will be gone.

Kenneth
 
#23
Thanks for the tip. The PT is pretty big so i dont know if the only vacuum machine I have access to may be able to do that. I will try. Anyway i think i have miswired it... I'm not sure.
Would I get 370Vac on the other two pins if it was miswired?
 
#24
Tell us how many primary and secondary taps it has.

If Leadbelly is too busy to calculate the plate and cathode resistor I'll do it; working for others gets me lazy though so you'll have to wait. Right now I'm not in the right mood for tube curves. 😱
 
#25
Sometimes there is a cardboard or wood wedge down the center leg of the E core. If this has come lose over time it will allow the core to vibrate. Easy to check unless the transfomrer has end bells. If it has end bells they should hold the outer edges of the cores tight.

A picture would be nice.

Hate 16 yo? Heck most of us are probably envious of you/remember when we were doing the same kind of things with old TV sets.
 
#26
You just don't know how many people think I'm a irresponsible moron just for being 16. It seems like when you turn 18 you stop being idiot.

I took some pics of the PT as you requested.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.


They are blurry but you get an idea of what is it. My photography skills just sucks, lol

Stalker, do it if you want... (I don't know how to say "no tengo prisa" in english 😛 )

Thank you all!
 
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#30
Not likely it is an OPT with that ratio. He has 380 out with 220 in. Reversing the leads would give 220:127.

Looks like a varnish dipped transformer.

You said the wire vibrates. Does the transformer actually make an audiable humming or buzzing noise?

If you power it up and let it set for 15 minutes, then unplug it. Is it hot?

Plastic bobbin usually does not use a wedge, but has sufficient E/I cores to make it tight.
 
#31
kavermei brings up an important point: if the PT has just 4 terminals, what is going to power the filaments of the 2 PCL86's? If the original poster can't buy additional tubes, he can't buy an additional transformer either. What was the FULL tube complement of the original amp? I am guessing there was one or more other tubes in series with the PCL86 tubes to make a non-mains-isolated series heater string.
 
#32
Actually, thinking about it some more, what is probably the case is that the power transformer is not a step up, but a step down. The console was probably wired so that the transformer stepped line voltage down to 117VAC, and then the tubes were wired as a 0.3A series heater string off the 117VAC, and B+ was generated off of the same 117VAC. In other words, the power transformer is just a means of adapting a ubiquitous American transformerless console design to 220VAC mains.
 
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#33
kavermei said:
Maybe a dumb question, but are you sure that it's not an output transformer? PTs from old tube gear usually have a more than 4 terminals.
Click to expand...
No, it is not. I've got 2 other transformers, they are smaller than the PT.
Here are some photos of the output trafos, one triple capacitor and the two tubes in there (The heatsink has nothing to do with the gramophone of wich I took the things of):
An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

Excuse the messy table blah blah-

TheGimp said:
Not likely it is an OPT with that ratio. He has 380 out with 220 in. Reversing the leads would give 220:127.

Looks like a varnish dipped transformer.

You said the wire vibrates. Does the transformer actually make an audiable humming or buzzing noise?

If you power it up and let it set for 15 minutes, then unplug it. Is it hot?

Plastic bobbin usually does not use a wedge, but has sufficient E/I cores to make it tight.
Click to expand...
What actually vibrates is not the wire, is the transformer. It doesn't get hot.

leadbelly said:
kavermei brings up an important point: if the PT has just 4 terminals, what is going to power the filaments of the 2 PCL86's? If the original poster can't buy additional tubes, he can't buy an additional transformer either. What was the FULL tube complement of the original amp? I am guessing there was one or more other tubes in series with the PCL86 tubes to make a non-mains-isolated series heater string.
Click to expand...
I can't buy more tubes because they don't sell them in normal electronics stores, but transformers are a very normal thing, and they will surely have lots of them, I can buy one if they are not too expensive.

I have attached too the original schematic where the valves were in-it has a schematic sheet glued into the gramopohone.

As I said above, it was from a gramophone, not an amplifier. It was stereo so it had 1 tbe for each R and L channels.

I'm definetly not sure of how the filaments were heated, but I think the trafo should not be giving me 380 volts, because the filaments, were if not directly, almost directly connected to the PT. Anyway I can power filaments with one LM317 or 1117 or 7812, you know.

And BTW, here is the original schem:
I did not changed the size of the photos for you to see clearly the photos, so I will put just a link to them:
http://img824.imageshack.us/img824/1/dscf1820q.jpg
http://img833.imageshack.us/img833/6863/dscf1821s.jpg
http://img535.imageshack.us/img535/1149/dscf1822.jpg <--- Best one.

 
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#34
To the last post wich I did not read:

No, this gramophone is ALL made in spain, designed etc, all.
So, It had an interruptor to set the voltage of the AC mains, I think here in spain a long time ago the AC mains only were giving 110V olr something like this, so the Switch you can see in the schem is not a SPST is a SPDT connecting one of the wires to 220V and one another to 110V....

But im not totally sure now that I think... IDK.
 
#35
That schematic shows that B+ is not isolated from the mains, so that is an absolute no-no, you must buy a transformer that can provide your B+ for the guitar amp and safely isolate from the mains.

The schematic shows the transformer as having 5 terminals, and that it is actually a 16VAC stepdown for the heaters of the PCL86's ONLY. Strange, as that is not matching your measurments or pictures.
 
#38
leadbelly said:
The schematic shows the transformer as having 5 terminals, and that it is actually a 16VAC stepdown for the heaters of the PCL86's ONLY. Strange, as that is not matching your measurments or pictures.
Click to expand...

Probably the "bottoms" of both windings are connected internally, bringing out only 4 terminals.

Yes it is a stepdown for the series stringed heaters.

Unfortunately as it is this transformer will be as good as useless. The only use I can think of would be to gap the core and use it as a choke...

K
 
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