From bernard–(at)–cn.nl Wed Apr 26 15:51:23 CDT 1995
Article: 1003 of alt.guitar.amps
Path: geraldo.cc.utexas.edu!cs.utexas.edu!howland.reston.ans.net!news.nic.surfnet.nl!ecnits.ecn.nl!ecnfac.ecn.nl!bernards
From: bernard–(at)–cnfac.ecn.nl (Marcel A. Bernards)
Newsgroups: alt.guitar.amps
Subject: Re: Old Fender diodes
Date: 26 Apr 1995 08:05:39 GMT
Organization: ECN – The Netherlands Energy Research Foundation
Lines: 71
Distribution: world
Message-ID: <3nkusj$f7--(at)--cnits.ecn.nl>
References: <3nin0l$63--(at)--wl.nstn.ca>
Reply-To: bernard–(at)–cn.nl
NNTP-Posting-Host: ecnfac.ecn.nl

In article <3nin0l$63--(at)--wl.nstn.ca>, poulo–(at)–ox.nstn.ca (XYZ) writes:

>Does anyone know the origin or specifications of the bullet-shaped
>solid-state diodes used in the the early (1960) Fender amps?

>The first generation circuit shows three of the diodes in series
>on each side of the AC secondary. When replacing these with new,
>high voltage diodes (IN4007), is it necessary to have three in
>series, too?

>Thanks,

>Ted

a 1n4007 has a 1000 Volt reverse voltage capability , but they are

if the voltage on the Caps is about +500 volt and the transformer voltage sine
wave goes to negative, the overall voltage is about 1000 volt over the diodes
The Fender has a dual coil transformer with a tap, an inheritance from
the tube diode era. that’s why you got that much voltage over the diodes.
So it could be done with one diode, but with very little margin left
So you need at least 2 in series, but they are dirt cheap,
so it’s hardly an issue to discuss what’s better.
2 or 3 in series ? Hell, I buy them in packs of 25 pieces at my local shop.

Newer amps have a single coil transformer and a Graetz style rectifier
with 4 diodes. They cannot be used in those older fenders, because
it needs a rewiring of the tranformer coil (parallel instead of in series)
because the windings needs to supply juice for both sine halfs.
It may be possible to split the coil tap in a fender transformer, but I’m not
sure, and it’s probably not worth the trouble.

Small ascii drawings to explain:

D1 D2 D3
+—>|->|->|—+ +500V
# L |
+—| 0V mass | Old style fender
# L |
+—>|->|->|—+
D4 D5 D6

+-+-+–>|——+ +500V
| | | |
| | +–|<--+ | # #| | Modern style rectifier. | | +--|<--+0V | | | | | +-+-+-->|——+

So you need at least 2 in series, but they are dirt cheap,
so it’s hardly an issue to discuss what’s better.
2 or 3 in series ? Hell, I buy them in packs of 25 pieces at my local shop.

Happy soldering

RP-1—(at)–CN.NL +—+
FTP.ECN.NL:/pub/DigiTech-Gear| Marcel A. Bernards
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[ RP-1 [_____] + + — Q Q ]| Also UNIX & Net SysAdmin–(at)–ECN.NL
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