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Post subject: Princeton Custom '68 Reissue Rectifier Swap
Posted: Thu Apr 12, 2018 2:06 pm
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Can I safely substitute a 5u4gb rectifier for the 5ar4 in a Princeton Custom '68 Reissue? Will the transformer handle the tube?


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Tue Apr 17, 2018 1:24 am
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The 5AR4 \ GZ34 will bring more 40 volts DC voltage .


Some voltage reading will say if it is ok for your amp.
To see if it safe for 6V6s
New bias is required

If you don't have any knowledge in electronic leave the original rectifier tube there.

Don't to this tube substitution


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Wed Apr 18, 2018 6:15 am
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The biggest concern is filament draw. A 5U4GB draws about 3 amps while a GZ34/5AR4 only draws about 2 amps. The question is, can the PT's filament windings handle a 3 amp draw.

UN


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Wed Apr 18, 2018 6:20 am
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upnorth2 wrote:
The biggest concern is filament draw. A 5U4GB draws about 3 amps while a GZ34/5AR4 only draws about 2 amps. The question is, can the PT's filament windings handle a 3 amp draw.

UN


I understand he want to use a 5AR4 so heater current will work . I'm I wrong ?


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Wed Apr 18, 2018 7:08 am
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Think he wants to go from 5AR4 to 5U4GB. If the modern PT is anything like the vintage ones, the switch can be done. In fact, many SF PR came with 5U4GB rectifiers.

http://www.thevintagesound.com/ffg/sche ... _schem.gif


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Wed Apr 18, 2018 8:14 am
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BMW2002Ti wrote:
Think he wants to go from 5AR4 to 5U4GB. If the modern PT is anything like the vintage ones, the switch can be done. In fact, many SF PR came with 5U4GB rectifiers.

http://www.thevintagesound.com/ffg/sche ... _schem.gif



Thank's, It is my lack of english speaking :(


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Wed Apr 18, 2018 9:56 am
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Maybe someone has run across a spec sheet for the '68 Custom PR's Power Transformer. The answer lies within.

Don't know what you're after but a 5V4 is always an option.

UN


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Tue Apr 24, 2018 5:57 am
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upnorth2 wrote:
Don't know what you're after ...
I suspect looking for something a bit stiffer and less spongey. I had my amp guy do that exact swap on a couple of old amps for that reason many years back. If memory serves, I believe the swap bought me about one and a half numbers on the volume dial before the onset of breakup, which I found to be quite significant.

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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Tue Apr 24, 2018 2:15 pm
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He has a 5AR4/GZ34 in it now and wants to switch to a 5U4GB.

The voltage drop with a GZ34 is roughly 10v while the dropping voltage of a 5U4GB is roughly 44v so he would get more "sag" from the 5U4, if that's what he's looking for. The world may never know.

UN


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Wed Apr 25, 2018 1:01 pm
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Thanks for the responses. Sorry for the late response back. Being out to town put me out of touch. Yes, UN. More sag is exactly what I wanted to A/B with the 5u4GB. I play blues harmonica and the swap was recommended for creating achieving just that. And, yes, the 3A filament draw is what concerns me. Tried finding more information about the custom Schumacher transformer in the new Custom '68 Reverbs without success. And BMW is correct Princeton did run the 5u4GB for a few years.

Well, I stuck it in there anyway just to see how it sounds. Didn't figure it would damage the transformer during a taste test. Didn't really care for the sound. I think they redesigned the new Princeton to sound a tad different than the Princeton's that preceded it. Not worth the swap.

Bushdog


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Wed Apr 25, 2018 9:02 pm
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With any rectifier type swap, you should really check your bias and plate/screen voltages as well as other tube voltages. You could experience enough change in the output section voltages to hinder performance. Usually a simple fix would be to alter the two dropping resistors value to get the best out of your output section.


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Fri Apr 27, 2018 4:57 pm
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I'm not interested in going through the whole re-bias scenario with a spanking brand new amp. I have some vintage amps that I've modded extensively for harp to achieve the tone I'm after. They were all cathode biased and I used a Weber Bias Right (or whatever it's called), which plugged into the tube sockets. None of them had a bias adjustment, so I changed out the resistor to get the tubes where I wanted them. Not sure how the fixed bias with the Princeton works, but I'm sticking with the stock rectifier. I don't think the 5u4GB would run the tubes hotter. If anything, I'm of the opinion that the tubes would run cooler. Pretty sure that the new '68 Custom Princeton Reverb's 6V6 Groove Tubes are actually JJs and that they are running pretty hot. No matter, I like the sound of the amp as is. I did stick a 12at7 in V4.

Bushdog


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Post subject: Re: Princeton Custom '68 Reissue Rectifier Swap
Posted: Fri May 04, 2018 7:10 am
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You might have better results doing that same swap with an actual reissue like the '65. The '68 Customs are not reissues, they are "Vintage Modified", and sound quite different compared to the reissues.

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