Noob Toob question

[hydro]

I have failed to resist the urge to tube roll: here is my question. Please bear with me as I understand as much about electronics as I do astrophysics:

Do preamp tube changes require bias adjustment, or just power tube changes?

My main amps are Mesas which are fixed bias, but I have an old Princeton reverb I am considering trying to make gig-worthy. It has never had its tubes changed since I've owned it (15 years?) and for all I know has the original tubes in it. Thinking about upgrading the original oxford stock 10" to a Weber and replacing preamp tubes with a 12AT7 or 12AY7.

And a refresh of the power section probably wouldn't hurt either.

The amp needs a little work anyway - has some noises sometimes and the reverb circuit craps out sometimes so if I replace the power section tubes I don't have a problem getting my tech to rebias.

Basically I want to make the amp handle higher volume cleaner with more tight bass response, while retaining that beautiful chime for cleans. This amp is the shiz nit, it really is the best sounding amp I have ever heard; am I tempting fate by jacking with it?

 

[Funkfingers]

Re: Noob Toob question

Pre-amp valves are self-biasing. Bias setting for your output stage valves will depend on which exact revision of Princeton you have.

Somewhere inside the cabinet of your amplifier, there should be a white printed label. This will itemise the correct valves for your amplifier. 7025, 12AX7, 12AT7 is a common permutation. Changing the 7025 to a 12AT7 or ECC82 will clean things up.

Earlier today, I purchased a pre-owned, non-reverb Blackstar HT-5H/HT-110 mini stack. Changing the Sovtek-made 7025 to a Seventies Mullard ECC82 (12AT7) reduced the gain and, hence, the overall output considerably. I tested various British and American valves. An old GE 7025 brought a Fender/Boogie quality. A mid Seventies Mullard ECC83 had that hard, slightly glassy quality for which Marshall used to be renowned.

The other thing that I did to improve the sound of the little Blackstar head was to run it through a MESA/Boogie Compact Thiele cabinet loaded with the mighty EVM-12L driver.

All in all, well-chosen valve and loudspeaker upgrades should do the trick.

 

[IM4Tone]

Re: Noob Toob question

As you change preamp tubes, give consideration to the 5751 in V1. It adds headroom and will not reduce the volume as much as a 12AT7 or 12AY7, plus I just prefer it's sound. Choosing the correct speaker replacement can make a huge difference. Choosing one with a higher efficiency (sensitivity) will give more volume at the same power output, so headroom is increased. Eminence speakers are known for very high efficiency on many of their models.

These are simple changes and ones I'd do for sure.

I'd also give consideration to changing out the speaker baffle to accommodate a 12" speaker. I've seen them advertised for the PRRI. There are so many more choices in 12" than 10" speakers and bass response is often better.

 

[hydro]

Re: Noob Toob question

Thanks for all the advice fellas!

I will probably just keep a 10" speaker since I have an extension cab on order (a StoneAge 1x12 cab - stoked!!!).

I looked at Weber 10" but the number of options is overwhelming. I will email them for suggestions though. Eminence OTOH seems to only offer a handful of 10" speakers. Rajin Cajun seemed interesting based on specs but I have no experience with them.

With these tube and speaker changes this could be my ideal "small room" rig, or for when my band plays more psych and less heavy sets. The preamp tube changes suggested by y'all seem like an easy upgrade, maybe a JJ 5751; I have used JJs in other amps and like them.

 

[Chickenwings]

Re: Noob Toob question

I have failed to resist the urge to tube roll: here is my question. Please bear with me as I understand as much about electronics as I do astrophysics:

Do preamp tube changes require bias adjustment, or just power tube changes?

My main amps are Mesas which are fixed bias, but I have an old Princeton reverb I am considering trying to make gig-worthy. It has never had its tubes changed since I've owned it (15 years?) and for all I know has the original tubes in it. Thinking about upgrading the original oxford stock 10" to a Weber and replacing preamp tubes with a 12AT7 or 12AY7.

And a refresh of the power section probably wouldn't hurt either.

The amp needs a little work anyway - has some noises sometimes and the reverb circuit craps out sometimes so if I replace the power section tubes I don't have a problem getting my tech to rebias.

Basically I want to make the amp handle higher volume cleaner with more tight bass response, while retaining that beautiful chime for cleans. This amp is the shiz nit, it really is the best sounding amp I have ever heard; am I tempting fate by jacking with it?

This is my kind of thread!

i gig with a princeton reverb II all the time and often i play in a jazz guitar duo with another dude who has a silverface princeton reverb.
Mine (the PRII) was built stock in a 1x12 combo and john got jealous of the extra fatness, so he had a new cab built (the old fender one had a crack in the baffle anyway) and his princeton is now in a 1x12 cab with a cannabis rex speaker (best speaker ever for low wattage fenders!). I'm jealous now of that speaker...mine is a kind of overwound greenback clone but the cannabis rex is really superb.
Sounds excellent. He also had the tube rectifier replaced some time in the 1980s with a ss rectification circuit to get some more punch and headroom. I think his princeton was around 12.5 watts and when the ss rectifier went it it was closer to 22 watts. You can get the same effect now non invasively with this:
http://www.tubedepot.com/ssr.html
or try one of these:
http://www.webervst.com/ccap.html
Keep all the regular type of tube types for the preamp tubes, just get fresh ones. The ss recto will give you the extra punch you need. If you do get a new set of tubes, i really like tung sols in the preamp for sparkle and jj's in the power section for extra headroom and low end.

fwiw...at 22watts with a 12 inch speaker, a princeton will do the job sweetly for plenty of gigs. It will break up nice and naturally at club volumes. One of the uses i have for it is in a 7 piece band with a 3 piece horn section and it keeps up nicely. Also its great for quieter stuff too cos you can get a sweet tone at low volumes. Here is a loose idea of how it goes in a biggish band:

I personally much prefer the sound of a 12, but if you do keep with the 10, then the ragin cajun is excellent. I put one in a friend's fender modelling something or other (i cant remember the model name) and it made a big improvement to its sound...only not as much as a 12 would have.

DO eet!

ps...there are some other cool things you can do to princetons to get different response and they are all easily reversible mods....but i wont go into the dark arts of princeton modding right now :naughty: