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Post by cedarchoper58 on Jul 5, 2022 18:16:08 GMT -5
can i put a Solid State rectifer in my Black Face Pro reverb without modifications? thks
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pdf64
Wholenote
Posts: 557
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Post by pdf64 on Jul 6, 2022 7:13:18 GMT -5
To replace a GZ34 / 5AR4?
That should be ok.
The HT voltage will rise a bit, but unless they’re getting ready to fail anyway, the HT caps should cope.
The output valve bias will need adjustment though. All else being equal, the current they pass will increase, and together with the voltage rising, they’ll idle hotter.
So the bias will need tweaking to cool things back down.
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Post by cedarchoper58 on Jul 6, 2022 17:34:41 GMT -5
To replace a GZ34 / 5AR4? That should be ok. The HT voltage will rise a bit, but unless they’re getting ready to fail anyway, the HT caps should cope. The output valve bias will need adjustment though. All else being equal, the current they pass will increase, and together with the voltage rising, they’ll idle hotter. So the bias will need tweaking to cool things back down. thanks i had read that SRV went to SS rectifer becuase when the amps got hot the sound got bad. Does this sound realistic thks |
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pdf64
Wholenote
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Post by pdf64 on Jul 6, 2022 17:42:30 GMT -5
It all depends on how the amp gets used.
If idling or being used at low power, it can be set to run a bit cooler, as the 10 watts from the rectifier’s heater has been saved.
If used at medium or high power, it may run hotter, as the higher voltage causes more current to be drawn, all else being equal.
I have a hypothesis that a significant cause of an amp sounding great initially then becoming flatter is that the speakers get hot. Folk focus on how hot their amp chassis snd transformers get, but never think to check the speakers. The voicecoil resistance increases as it gets hotter, causing characteristics to change, and the amp’s ability to deliver power to it will diminish to some degree.
The use of speakers with heavy duty magnets and voicecoils should help to mitigate that.
Conversely, neo type speakers may exacerbate the issue, as their tiny magnets have so much lower thermal mass. ie they’ll heat up quickly.
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Post by rdr on Jul 7, 2022 20:05:15 GMT -5
You could try a Weber Copper Cap. Power tranny will run cooler, and you can choose the amount of sag or no Sag. I've been running in Fender amps for awhile with no problems. Such as: www.tedweber.com/wz34/ |
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pdf64
Wholenote
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Post by pdf64 on Jul 8, 2022 17:44:09 GMT -5
I’m not super keen on Weber Copper Caps, but then I’m a big fan of actual valve rectifiers.
The WZ34 I had drops a lot more voltage under load than a real GZ34. The internal dropper resistor seems to be chosen to achieve the same idle voltage, ie a low current draw. Real rectifier valves don’t have a linear resistance characteristic. The WZ34 knocks about 15W off the output of a typical 50W type amp.
It seems a very bad thing that the copper case isn’t grounded. If the internal resistors failed and shorted to the case, it would be a significant hazard.
And the copper case came off mine, exposing the high voltage internal parts.
I suppose that the glass bulb on valves can break, exposing the same hazard.
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Post by pcalu on Jul 10, 2022 7:25:48 GMT -5
The question is why? I'm not pro or con SS or tube rectifiers, I like the feel and sound of both. But, a GZ34 IMHO is about as SS as it get's without going SS. Using a good GZ34 get's you very consistent voltages with little sag. (isn't that what someone is looking for in a SS rectifier?) Then why would you want to mod a pre CBS? You must have the complete opposite taste than me.  I love the Pro reverb.. think it might be the best amp Fender made. I prefer an early non master Silverface because of the 5U4GB... it sags right were I want an amp to sag. Very early Marshall'ish in nature. |
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Post by Leftee on Jul 10, 2022 7:28:36 GMT -5
I’ll add, if you feel that your amp is “dulling out” over a gig, it might want a new rectifier tube.
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pdf64
Wholenote
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Post by pdf64 on Jul 10, 2022 19:10:49 GMT -5
Maybe a better SRV mod for a Pro would be a beefier OT. eg Bassman type. Those little stock OTs can have a nice tone, but a beefier OT may provide a noticeably bigger, more solid tone.
It’s not nice to mod nice old amps though.
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Post by Lesterstrat on Jul 21, 2022 12:06:44 GMT -5
If you’re looking to tighten the sag up a bit, change the PI tube. I think that’s the right one. I had an amp that had a bit much sag for my liking and the the gentleman that owns KCA Tubes (can’t think of his name) turned me on to simply changing the PI tube (almost certain that was it). You can always double check that point, but my point is it might easier to go that route regardless of the actual tube position rather than converting to a SS
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pdf64
Wholenote
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Post by pdf64 on Jul 22, 2022 4:29:57 GMT -5
Dunno how the valve in the phase splitter circuit might affect sag, but I suppose valves can have weird failure modes.
To check this, if the reverb sounds fine, then the 12AT7 in the V3 reverb driver is probably good. So if the 12AT7 valves in V3 and the V6 phase splitter sockets are swapped over, and the reverb still sounds fine and the amp still sags at high power outputs, then the sag probably isn’t due to the phase splitter valve.
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I love the Pro reverb.. think it might be the best amp Fender made. I prefer an early non master Silverface because of the 5U4GB... it sags right were I want an amp to sag. Very early Marshall'ish in nature. 
