100 watt not bridge rectified Marshall

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aerojazz
Senior tube assistant
Posts: 171
(3/10/04 7:49 pm)
 100 watt not bridge rectified Marshall
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 Hey group, Does anyone have a schematic of a pre-metalface 100 watt(plexi)? Not model 1959, evedently my PT goes into two diodes NOT a bridge rectifier. I need to see how to come off of the diodes. and how to configure the filter caps. I've been wizzing in the breeze here for a few days.

Any help will be appreciated
 
Lucid Alice
Senior tube assistant
Posts: 178
(3/10/04 8:14 pm)
 Re: 100 watt not bridge rectified Marshall
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 Any 50 watt plexi rectifier should be identical as far as the diodes. The filter caps should be as you have now.

Just look through Doug's library, it's all there.
 
aerojazz
Senior tube assistant
Posts: 172
(3/10/04 8:44 pm)
 Re: 100 watt not bridge rectified Marshall
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 Can I use a bridge rectifier without coming of the ground pin.
In other words what I'm doing now. Is this basicly the same as using two diodes?
 
ganzonimx
Hey get your own solder
Posts: 427
(3/10/04 9:01 pm)
 Re: 100 watt not bridge rectified Marshall
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 If you have a center taped PT you have to use a full wave rectifier, with two diodes (ore more diodes in serie like in Fenders) and the center tap to ground.

If you have a PT without a center tap, use a bridge rectifier. The negative pole of the bridge rectifier connects to ground.

Either transformers work perfectly, the type of PT determines what rectifier you will need.

Cris
 
aerojazz
Senior tube assistant
Posts: 173
(3/11/04 7:21 am)
 Re: 100 watt not bridge rectified Marshall
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 Q:
Is using a bridge rectifier but eliminating the neg. pin to ground the same as a full wave rectifier?

I believe this is what TinyDaddy was implying. I need to understand-know that this is the case.

Yes my PT does have a CT and yes when I removed the wire from the neg. pin to grnd. the B+ voltage did devide.

What I'm trying to understand is this :
Can I use the bridge in this way instaed of using two
diodes to accomplish "Full wave rectification"?

Edited by: aerojazz at: 3/11/04 7:26 am
 
GroundhogKen
Forum Moderator
Posts: 2314
(3/11/04 8:17 am)
 Re: 100 watt not bridge rectified Marshall
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 Yes,

A bridge rectifier with the (-) negative pin left unconnected is the same as a full wave rectifier if you ground the power transformer center tap.

However, the transformer required to get 450v B+ with a two diode full wave is about 330-0-330vrms. Using a proper bridge rectifier you would get 450 B+ with 165-0-165vrms with the center tap ungrounded. So, a transformer specified for a bridge is usually not suitable for full wave operation.


Ken
 
aerojazz
Senior tube assistant
Posts: 174
(3/11/04 10:45 am)
 Re: 100 watt not bridge rectified Marshall
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 Great Ken, What I have is a PT designed for full wave (two diode) rectification. I am attemting to use the bridge in the mannor above. I do see the correct voltage and just wanted to make sure I was not going to burn something up.

My CT is grounded at the main bolt now. and not at the filter caps like I thought it was suposed to be.(Marshall 1959 model)

When I had the CT at the filter caps the B+ voltage went down a little, but seemed to be alittle higher at the plates of the preamp tubes.
any reason?

 
 
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