Princeton Reverb Reissue - time for some changes maybe

Gagaryn

I've had my Blackface PRRI for a while now and whilst it sounds absolutely the nuts with Fender single coils with humbuckers it really is too bassy, even with the bass pot all the way down. Also the reverb is great but there is just too much - over 3 on the dial is overkill so dialling in the exact right amount needs a delicate touch. Any suggestion for improving both or either?

octatonic

It has been discussed a lot since they reissued it.

There are a bunch of mods available for it here: http://www.ratvalveamps.com/fender-princeton-reverb

I cut my losses and got rid of.

No point spending several hundred quid to sort out the issues.

ICBM

Too bassy?! Too much reverb?!! Impossible.

Suggestion - bring it to me and I will dispose of it in an environmentally responsible fashion. In fact, I'll even come and collect it if you prefer.

Try changing V3 to a 12AT7, 12AY7 or even a 12AU7 . (The 12AX7 next to the reverb transformer on the side next to the power valves, directly below the footswitch jack on the reissue.) That will brighten the dry tone and reduce low-end slightly, and lower the reverb return gain - luckily both are done with the same valve.

I'm not sure what 'issues' there are - it's a classic amp for a reason. I was working on an original one a couple of weeks ago - a very sweet thing… yes, pretty bassy and with not all that much headroom, but to me that's a lot of the beauty of them - you can get a really fat overdrive tone at sensible volume. The only problem I find is not quite enough clean headroom - but that can be improved a bit, with the 'Stokes mod'.

Gagaryn

John, thanks for the offer - you really are too kind. Unfortunately, I've just stuck a 12AY7 in V3 like you suggest and that has done the trick - tried it with my bassiest 'bucker guitar and it's perfect, tried it with a tele and realised that it might have made a bit much of a difference. I'll get a 12AT7 and that should be about right with a bit of luck. Thanks for the help.

p90fool

I have a similar problem with my 68 Custom Princeton - I'll give that a go, I assume all that part of the circuit is pretty much the same?

ICBM

Gagaryn said:

John, thanks for the offer - you really are too kind. Unfortunately, I've just stuck a 12AY7 in V3 like you suggest and that has done the trick - tried it with my bassiest 'bucker guitar and it's perfect, tried it with a tele and realised that it might have made a bit much of a difference. I'll get a 12AT7 and that should be about right with a bit of luck. Thanks for the help.

Foot… aim… shoot… damn.

Loobs

I find they're greatly improved with a 12" speaker like the Headstrong Lil' King. 

EdGrip

Exactly - obviously you need to get a 12" speaker in there too.

p90fool

I actually think the 10 suits it better tbh, but might have a rethink when I start messing with valves.

jpfamps

octatonic said:

It has been discusses a lot since they reissued it.

There are a bunch of mods available for it here: http://www.ratvalveamps.com/fender-princeton-reverb

I cut my losses and got rid of.

No point spending several hundred quid to sort out the issues.

Whilst most of these mods seem sensible, I'm always fairly sceptical about changing capacitor types.

Furthermore silvered Mica caps are notorious for leaking DC, so probably shouldn't be used in any part of the amp as DC blocking caps.

benecol

ICBM said:

Try changing V3 to a 12AT7, 12AY7 or even a 12AU7 . (The 12AX7 next to the reverb transformer on the side next to the power valves, directly below the footswitch jack on the reissue.) That will brighten the dry tone and reduce low-end slightly, and lower the reverb return gain - luckily both are done with the same valve.

Mind-blowingly good tip: I've had a secondhand PRRI since September, and always been somewhat narked by the amount of reverb hum. It's been back to Fender, who described it as being "what they'd expect from this amp", and to a local tech, who took some of the reverb wiring off the circuitboard, confirmed there were no problems, and said that it was "as good as it was ever going to be".

That said, the hum that came through with the reverb above about 3 has always been enough to bug me. Yes, it's only audible at low volumes (sadly, the volume I'm playing at most of the time) and yes, above 3 it's a pretty daft amount of reverb anyway, but I'd like the option to crank it up anyway. Which is a bit OCD of me, I suppose.

All that said, switching in a spare 12AT7 (ironically, one I'd bought for the other side of the reverb circuit) as you suggested has really calmed it down! Can I just ask, in layman's terms, what's changed? What's it done to the reverb circuit? Do I need to get it rebiased or owt (it's a newish, matched set of JJs in there)?

But mainly: thanks for the top tip - WISDOM GIVEN x

Gagaryn

Glad that's helped but the reverb shouldn't be humming like you describe, mine is dead quiet, there is a tint bit of background noise with vibrato though. ICBM will be able to explain much more thoroughly but changing the V3 tube for a similar tube with less gain will reduce the voltage in that part of the circuit. And there is no need to rebias unless you make changes to the power tubes - that's the two 6V6's next to the rectifier at the other end of the chassis.

menamestom

p90fool said:

I actually think the 10 suits it better tbh, but might have a rethink when I start messing with valves.

+1.  I looked at mods for mine but then realised what the amp is, a smallish vintage style practice amp with some good Fender mojo.
Okay for small gigs but for bigger gigs it has a bigger brother with a 12" speaker and stiffer power supply already.

The smallish speaker and relatively underpowered output transformer are part of the charm IMO, no point spending a small fortune on the amp then changing it into a Deluxe Reverb. 

I used to run mine through a 12" inch Celestion gold in a bigger extension cab now and again, the bass was a little better (comparing to a 10" Eminence Ragin Cajun here) but the bass was still flubby.  I think to cure this properly you need to look at the BillM upgraded output transformer and other mods.

Personally I think even with the stock speaker, the amp sounds ace, it's just that it has a very definite sweet spot (about 3 - 4 volume and 2-3 Reverb) and if you use it out of these parameters in becomes quickly apparent that it has it's limitations.

p90fool

menamestom said:

p90fool said:

I actually think the 10 suits it better tbh, but might have a rethink when I start messing with valves.

+1.  I looked at mods for mine but then realised what the amp is, a smallish vintage style practice amp with some good Fender mojo.
Okay for small gigs but for bigger gigs it has a bigger brother with a 12" speaker and stiffer power supply already.

The smallish speaker and relatively underpowered output transformer are part of the charm IMO, no point spending a small fortune on the amp then changing it into a Deluxe Reverb. 

I used to run mine through a 12" inch Celestion gold in a bigger extension cab now and again, the bass was a little better (comparing to a 10" Eminence Ragin Cajun here) but the bass was still flubby.  I think to cure this properly you need to look at the BillM upgraded output transformer and other mods.

Personally I think even with the stock speaker, the amp sounds ace, it's just that it has a very definite sweet spot (about 3 - 4 volume and 2-3 Reverb) and if you use it out of these parameters in becomes quickly apparent that it has it's limitations.

My thoughts exactly, I just embrace what it is, because it's fantastic at it. I have other amps for other purposes.

ICBM

benecol said:

All that said, switching in a spare 12AT7 (ironically, one I'd bought for the other side of the reverb circuit) as you suggested has really calmed it down! Can I just ask, in layman's terms, what's changed? What's it done to the reverb circuit?

It's reduced the gain in the reverb return amplifier, so both the amount of reverb signal and the hum picked up by the transducer (which is basically a single coil pickup) are reduced. It's also reduced the overall gain of the amp slightly because the other half of the valve is used for the whole signal after both the reverb and the dry signal are mixed together - so the effect on the reverb is doubled relative to the dry signal.

If hum is still a problem, try moving the amp around - it can often be very location-dependent exactly because it is basically single-coil pickup hum.

You don't need to rebias it, the preamp valves operate in cathode (self) bias so it will automatically compensate. Be careful with just substituting different types in general though, there are a few circuit locations in some amps which won't like it and you could blow the valve or at worst a component in the amp. This one should be fine because it's just a simple twin gain stage driven from a fairly low supply voltage.

benecol

Once again, thank you very much.

p90fool

Just put a 12AY7 in V3, perfect!

Cheers @ICBM

thinline72

Apparently, I have a pretty similar problem with my Custom 64 HW Reverb (mainly the excess of bass). Or maybe it's just my head room is too small for it...

Anyway, I'd like to give it a try but as I'm complete noob and never changed tubes in the amp, I would much appreciate some advice on that.

I have JJ 12AT7 in my Tube Drive that I can try + RCA 12AV7 and JJ 5751. AFAIK, they are all interchangeable, right? But @ICBM haven't mentioned the last two in the post, so wanted to confirm if it's OK to try with them too?

Also, tubes location seems to be a bit different in 64, but if I got it right V3 is the 3rd one from right to left (if look from the back of the amp)? In case of 64 it's under metal cover which I'm not quite sure how to remove safely... Or is location fully different in 64?

ICBM

thinline72 said:

I have JJ 12AT7 in my Tube Drive that I can try + RCA 12AV7 and JJ 5751. AFAIK, they are all interchangeable, right? But @ICBM haven't mentioned the last two in the post, so wanted to confirm if it's OK to try with them too?

Yes, you can substitute any of the 12A*7 family for a 12AX7 *as long as the plate resistors are adequately rated*. I'm pretty sure they are in these - there have been some problems with them in a couple of Fender reissue amps, especially the '59 Bassman where fitting a 12AY7 (ironically, the correct original type in the 1950s) in V1 can cause trouble.

thinline72 said:

Also, tubes location seems to be a bit different in 64, but if I got it right V3 is the 3rd one from right to left (if look from the back of the amp)? In case of 64 it's under metal cover which I'm not quite sure how to remove safely... Or is location fully different in 64?

V3 is the third from the right.

To get the cover off you push it up very slightly and rotate anticlockwise - if you were looking from underneath - about an eighth of a turn... it's a 'reverse bayonet' type fitting.

thinline72

Thanks @ICBM ! I'll try to find some courage and give it a shot!

I assume it's safe enough to do in terms of voltage and other things as I only want to change the tube 

ICBM

thinline72 said:

I assume it's safe enough to do in terms of voltage and other things as I only want to change the tube 

Yes, although it's always better to set modern Fender amps (those which have the option, which this one does) to 240V mains voltage rather than the 230V they come set to. This entails taking the chassis out though, so not something you automatically have to do to change a preamp valve. That makes the amp run cooler and slightly more reliably in the long term.