LARGE diodes in the Ampeg V4?

[t***@aol.com]

i have a 1977 Ampeg V4 i'm going through. It has 2 LARGE diodes (rated
at 1amp 1400v) in series off each side of the plate supply of the
output transformer. I've seen schematics with them on there, i've seen
them without.
Are they necessary? if so what should i replace them with? the IN4007
is 1 amp 1000v, don't know of anything like them rated higher...

any help would be great.


thanks

[Stephen Cowell]

Post by t***@aol.com
i have a 1977 Ampeg V4 i'm going through. It has 2 LARGE diodes (rated
at 1amp 1400v) in series off each side of the plate supply of the
output transformer. I've seen schematics with them on there, i've seen
them without.
Are they necessary? if so what should i replace them with? the IN4007
is 1 amp 1000v, don't know of anything like them rated higher...
any help would be great.

You can series diodes for more voltage rating...
if the diodes are *very* similar, you can get
away without putting bypass caps on them.
Fender used 3 in a string for the BF-SF amps x2.

What are those, flyback diodes? BTW you
described it, these aren't the main HV rectifiers,
are they? *All* tube amps have those.

Of course, if you've got your dick-skinners inside
this thing, you'd better already know this stuff.
Be vewwy caweful...
__
Steve
.
worth what you paid

[m***@yahoo.com]

YES THEY ARE necessary, these diodes prevent oscillation in the
output stage
and will be found in marshall schematics, as well.

[jh]

Post by m***@yahoo.com
YES THEY ARE necessary, these diodes prevent oscillation in the
output stage
and will be found in marshall schematics, as well.

pfffffffffftttt

[Dave Curtis]

Post by t***@aol.com
i have a 1977 Ampeg V4 i'm going through. It has 2 LARGE diodes (rated
at 1amp 1400v) in series off each side of the plate supply of the
output transformer. I've seen schematics with them on there, i've seen
them without.
Are they necessary? if so what should i replace them with? the IN4007
is 1 amp 1000v, don't know of anything like them rated higher...
any help would be great.
thanks

Are they bad?
-Dave

[Lord Valve]

Post by t***@aol.com
i have a 1977 Ampeg V4 i'm going through. It has 2 LARGE diodes (rated
at 1amp 1400v) in series off each side of the plate supply of the
output transformer. I've seen schematics with them on there, i've seen
them without.
Are they necessary? if so what should i replace them with? the IN4007
is 1 amp 1000v, don't know of anything like them rated higher...
any help would be great.
thanks

Flyback diodes.

They're looking for a combined 2,800 volt PIV;
the current rating isn't critical. You can replace
them with three 1N4007 (or similar 1,000 PIV
parts) if they are shorted.

LV

[t***@aol.com]

Post by Lord Valve

Post by t***@aol.com
i have a 1977 Ampeg V4 i'm going through. It has 2 LARGE diodes (rated
at 1amp 1400v) in series off each side of the plate supply of the
output transformer. I've seen schematics with them on there, i've seen
them without.
Are they necessary? if so what should i replace them with? the IN4007
is 1 amp 1000v, don't know of anything like them rated higher...
any help would be great.
thanks

Flyback diodes.
They're looking for a combined 2,800 volt PIV;
the current rating isn't critical. You can replace
them with three 1N4007 (or similar 1,000 PIV
parts) if they are shorted.
LV

hello, thanks for the help.
yes they must be "flyback" diodes

no, i don't think they are bad, the amp is just 30years old. i was
replacing all the original diodes and specifically noticed some V4
schematics had them and some don't.

[t***@aol.com]

I don't want to start another thread(yet) so i thought i'd ask here.
this amp was long ago converted from 7027 to 6550 tubes(before any
7027 reissues were available....)
using the instructions in the pittman tube book.
That book disintegrated long ago....
can anyone send me the instructions, just so i can verify that it is
still setup correctly?
(i paid for the book, honest....) it's been to a few techs and i'm not
sure what each and every one did.
or is there a better setup for the 6550 conversion out there?

again, thanks for the help.

Post by t***@aol.com

Post by Lord Valve

Post by t***@aol.com
i have a 1977 Ampeg V4 i'm going through. It has 2 LARGE diodes (rated
at 1amp 1400v) in series off each side of the plate supply of the
output transformer. I've seen schematics with them on there, i've seen
them without.
Are they necessary? if so what should i replace them with? the IN4007
is 1 amp 1000v, don't know of anything like them rated higher...
any help would be great.
thanks

Flyback diodes.
They're looking for a combined 2,800 volt PIV;
the current rating isn't critical. You can replace
them with three 1N4007 (or similar 1,000 PIV
parts) if they are shorted.
LV

hello, thanks for the help.
yes they must be "flyback" diodes
no, i don't think they are bad, the amp is just 30years old. i was
replacing all the original diodes and specifically noticed some V4
schematics had them and some don't.

[Ned Carlson]

Post by t***@aol.com
I don't want to start another thread(yet) so i thought i'd ask here.
this amp was long ago converted from 7027 to 6550 tubes(before any
7027 reissues were available....)
using the instructions in the pittman tube book.
That book disintegrated long ago....
can anyone send me the instructions, just so i can verify that it is
still setup correctly?
(i paid for the book, honest....) it's been to a few techs and i'm not
sure what each and every one did.
or is there a better setup for the 6550 conversion out there?
again, thanks for the help.

AFAIK, if the bias voltage is what the schematic says
it should be, you're OK. The bias current on these amps is very low,
even with 6550's installed, if the bias voltage is right.

A long time ago someone pointed out that the "official"
Ampeg kit for refitting these amps with 6550's solely consisted
of new base clips, and nothing for modding the bias circuit
at all. OTOH, these amps have what's called a "capacitive
divider" for bias, rather than an actual bias tap, so checking
the bias voltage is a real good idea, just in case any of the
components in the bias circuit have crapped out.

The "flyback protector" diodes came later, Ampeg probably
got tired of making warranty replacements on blown output
transformers caused by drunk dips tripping over speaker
cables while someone was wailing full volume on the amp.
Diodes are a lot cheaper than transformers.