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FDP Forum / Amp Mods, Repairs, and Projects / Edumacate me on different rectifiers in a black face Deluxe Reverb


What It Was!

Fairly Unbalanced
Dec 10th, 2017 04:45 PM   Edit   Profile   Print Topic   Search Topic

Supposedly they change the feel of the response when you go with different value tubes… I’m not qualified to bias the amp if it needs it, just trying to learn a little bit.


on the rhine

Dec 11th, 2017 03:07 PM   Edit   Profile   Print Topic   Search Topic

Hi Dolemite!

The stock rectifier-tube is a GZ34 (or 5R4 if I have that right...).
You CAN use other tubes (5U4, or even 5Y3), but you have to check if the voltages are in line and - possibly - adjust the bias.

Personally, I would rather experiment with the pre-amp tubes - like, pulling the first tube of the unused channel (more gain to the used channel) or substitute the phase-inverter tube (last pre-amp tube) for a 12AX7 instead of a 12AT7 for more gain/breakup...

cheers - C.



Dec 12th, 2017 04:17 AM   Edit   Profile   Print Topic   Search Topic

The stock rectifier is GZ34 / 5AR4, which is the least lossy rectifier type.
Assuming that your current GZ34 is functional, any other rectifier will reduce the HT and hence create a cooler bias condition, so can be swapped in without concern that the power tubes will run hot.
They will make the amp's high volume response more saggy and reduce the power output, the point being that you're not going to notice much difference unless you play loud.

The alternative rectifier types include 5V4, 5U4, 5R4 and 5Y3.
None of those are without potential issues but experience has shown that they are unlikely to cause an actual problem.
These are that a 5U4 will draw a bit more power from the amp's power transformer, and with the others, the amp's circuit may cause one or more of the tube's limiting values to be exceeded (reservoir cap value, input voltage).

Note that current production 5Y3 are thought not to comply with type characteristics, ie they are likely a similar Russian tube type that has been re-labelled, and they put out more voltage than a vintage USA made item. Given your application that isn't likely to be an issue, as they will almost certainly be saggier than a GZ34.


What It Was!

Fairly Unbalanced
Dec 12th, 2017 06:27 AM   Edit   Profile   Print Topic   Search Topic

Thanks guys. Carsten, that's where I went first. Picked up a used Marsh BFDR and tried a few swaps.. sounds even sweeter now.

It appears that the bottom line on rectifier swaps is that the safe way to do it is to have our local amp tech measure the voltage of a potential change. Don't want to cook NOS power tubes or PT, they ain't cheap!

Contributing Member


All I need is one more guitar
Mar 20th, 2018 07:25 AM   Edit   Profile   Print Topic   Search Topic

Carsten mentioned the idea of pulling a preamp tube from the Normal channel.
Is that V1 ?
Could I just leave it out permanently?

FDP Forum / Amp Mods, Repairs, and Projects / Edumacate me on different rectifiers in a black face Deluxe Reverb

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