Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: pgussler on April 02, 2022, 05:15:17 pm

Title: Late 60's 50W Marshall Bridge Rectifier Specs
Post by: pgussler on April 02, 2022, 05:15:17 pm

Does anyone have the specs for the bridge rectifier found on a late 60's Marshall 50W Lead.  Part number is IIR GB256/PA 70 21.  Thanks in advance.

Title: Re: Late 60's 50W Marshall Bridge Rectifier Specs
Post by: pgussler on April 02, 2022, 05:37:32 pm

Never mind - found it.   1000v 25A

Title: Re: Late 60's 50W Marshall Bridge Rectifier Specs
Post by: PRR on April 02, 2022, 05:42:44 pm

25A seems mighty generous, especially for late 1960s.

I absolutely approve of greatly over-speccing rectifiers. I used to get paid salary to replace marginal rects but that job is gone. Meanwhile the costs (labor and headache) of replacing will cover a heap of over-speccing so you never have to replace it.

Just be sure it can be made to fit.

Title: Re: Late 60's 50W Marshall Bridge Rectifier Specs
Post by: pgussler on April 03, 2022, 04:06:04 am

Agree on the amperage generosity and also on the overbuilt approach.  The failed unit is a big sucker to begin with and the dimensional specs from the data sheet for the replacement part indicates it will plop down right in its place.  Thanks for the reply.

Title: Re: Late 60's 50W Marshall Bridge Rectifier Specs
Post by: pdf64 on April 03, 2022, 04:32:25 am

1kV is marginal.
Perhaps that’s why the original failed?
Bear in mind only 2 of the 4 diodes in the FWB package are in circuit.
My take is that even just 2 series pairs of 1N4007 would be better.

Title: Re: Late 60's 50W Marshall Bridge Rectifier Specs
Post by: pgussler on April 06, 2022, 04:56:09 am

Thanks for the follow up.  All points well taken.

Title: Re: Late 60's 50W Marshall Bridge Rectifier Specs
Post by: pdf64 on April 09, 2022, 06:09:36 pm

Here’s report of 1kV diodes failing https://ampgarage.com/forum/viewtopic.php?f=9&t=35385