Help with questions to ask Amp Tech & request list

[MikeJr.]

Greetings from a new member,

I'm thinking that maybe the answer to my questions have already been discussed here, but I haven't been able to find relevant posts.

Here is my problem: I am the original owner and periodic player of a 1969 Fender Princeton Reverb. Lately, I have been playing much more and find the tone to very nice when volume is around 4. At higher levels it hurts my ears with too much treble. The amp has never been serviced. I am not able to do electronic work and want to take the amp to a tech to: replace tubes with JJs, put a new Weber 10F150T (light dope, 25 watts) and do whatever else one should do to help the amp "get right". I'm not interested in Mods and will keep all parts in order to convert the amp back to original parts if I need to at some point. I also see that one spring in the two spring reverb tank is broken (it looks like the "hook" where the spring hooks on at the end of the tank has broken off and this looks very hard for me to see how anyone could re-solder the connection).

So, here is the first question. I have identified two reputable guitar stores who work on amps and my guitar tech recommends an audio and sound electonics store here in town (honolulu). I'd like to figure out the right questions to ask of each three in order to make the decision on who would be best able to work on this Fender Princeton Reverb amp. In other words, how important is previous experince with this amp or fender amps or whatever.

Secondly, once I identify the person to do the job, what do I ask that person to do/check/replace other than what I've identified above. I'd like to have the amp thoroughly checked out/fixed and have no ability to speak "amp-ese" other than what I have stated in the paragraph above! I REALLY need a laundry list of things that should be checked or an appropriate idea of how to generally ask the tech to very thoroughly fix this baby up. For example, a couple of the knobs controlling the volume and treble/bass, etc. make crackling noises as I turn them. (I'm hoping to watch the person do the work if possible just to learn a little more).

Should I stick with this reverb tank (which does work okay on one spring) or replace?

If anyone can guide me through this process, I would really appreciate it. I guess an inevitable next question would be: what kind of ongoing maintenance should I do once I have the amp playing right?

I apologize for all of the questions.

Thanks,

Mike

[pontiacpete]

I would ask some of the local musicians who they recommend for amp repair. Go out to some of their gigs and ask players who are using fender amps , vintage ones if possible.

[gbono]

Looks like you already have a partial list of repairs that need to be made. Since amplifiers are rated in a completely subjective manner - how it sounds - than you are going to be the one to say what does or doesn't sound right. I would also suggest having the output of the amp connected to a scope before and after any changes are made.

Your amp is 40 years old and should have some preventaive maintanance done in the form of new tubes and their associated re-biasing, power supply filter caps should also be replaced, cleaning and tightening any controls or jacks/socket pins,visual inspection, I would also replace the power cord with a proper three conductor (i.e. grounded) one, disable the polarity switch, etc, etc.

[pontiacpete]

the reverb tank is something you can replace yourself. The fender princeton uses an accutronics 4AB3C1B.
I have a princeton that's about the same age as yours. I regret to say that many years ago I changed the 10" speaker to a 12", dumb move, but most of it is original. THe filter cap can is original and most of the other caps are original. It has a great sound.
I find that this amp when played up around 4 or 5 starts to break up alot. Most guys like this sound. I rarely use it for that purpose> I use it mostly for jazz gigs or duos where I don't want a overdriven sound.
If I were you, I wouldn't bother changing the speaker if it works, that old fender speaker is probably fine

good luck

[Dave Curtis, dB AudioTech]

Welcome to the group!

1) Make the amp safe. Have a 3-conductor cordset installed if it hasn't been done. Make sure the neutral conductor goes straight to one of the power transformer's primary wires, and the "hot" conductor goes through the fuse, the switch and then to the other primary wire. Make sure the neutral is connected to the wide slot on the rear AC receptacle; Fender wired these backwards for a number of years.

2) If the tech can't measure the ESR (equivalent series resistance) of the electrolytic caps, have him replace all of them.

3) It's possible that the tech may be able to reattach the broken reverb spring; a new tank will run about $40 (or more in HI).

4) Don't replace the small signal caps unless they're causing problems.

Hope this helps.

[Euthymia]

I know you said you're not interested in mods for this amp, but adding an adjustable bias pot is the biggie I do on SF Princeton Reverbs.

Correct bias is important to the tone you get when it's turned up (If your amp is biased too cold, it could make for some harshness), and it also helps the trem if you use that.

If the tech needs to put new tubes in it, the "Tung-Sol reissue" 6V6's are my favorite vintage-sounding new tubes.

[Enzo]

And having worked on your exact model amp is not so important. AMps are amps, and they all work the same way. Any COMPETENT tech will know what to do.

[pontiacpete]

I gave you the wrong info
the tank for the princeton is here and is $26. Just ordered one myself

Accutronics 8AB2A1B Reverb Tank

[Dave Curtis, dB AudioTech]

Last I checked, Accutronics was selling on eBay, but I found what I was looking for cheaper somewhere else...

[MikeJr.]

Thanks for the advice

I appreciate the help. Particularly about the reverb tank. I think I have enough info walk (talk) myself through the process of getting the amp checked out.

I have seen a number of posts suggesting that this amp will benefit from a new speaker. As I recall, the original speaker was re-coned sometime in the early 70's and I think I'd feel more comfortable with a direct (i.e. 10") replacement.

Aloha

[MWJB]

Here's a list of things I'd expect any tech to check out in the course of/before a service:

1 Sound - Quality, unusual noise, microphonic valves?
2 Pots - Noisy/intermittent?
3 Reverb
4 Tremolo
5 Fuse - Correct type, current & voltage rating?
6 Valves - Age, manufacture, correct specification?
7 Speakers - Manufacturer, correct ohmage & polarity?
8 Components - Burnt, loose or poor connections?
9 Electrolytics - Cathode bypass & bias supply caps?
10 Power Supply Filter Caps - Correct values, age & wiring?
11 Valve Sockets - Damage, signs of arcing?
12 Heater Wiring (inc. 2x100ohm virtual CT)?
13 Transformers - Correct parts, signs of overheating?
14 Output Transformer - Check turns ratio?
15 Output Plate Voltage?
16 Screen Voltage/Resistors?
17 Preamp Plate & Cathode Voltages?
18 Bias Current - Within perameters, matched valves?
19 Heater Voltage?
20 Board Conductivity?
21 Modifications?

This treble that hurts your ears, is it something that has recently started, or is it something the amp has always done? Do other Princeton Reverbs do the same thing? I ask because a service might not change this specifically. If it is an inherant feature of the amp you may want to consider a minor mod.

As Enzo says, there is nothing unusual about the PR, any competant tech with reasonable experience will know what they are doing.

"(I'm hoping to watch the person do the work if possible just to learn a little more)." The tech may be open to this idea, or he may not. Either way it is no indicator of his abilities or trustworthiness. I don't mind carrying out checks in front of a client & advising as I go, but I don't expect to babysit them throughout a whole cap job (I can't guarantee that I will be in a position to do the work at a time that they are free), or have them butting in every 5 minutes asking what I am doing...I'd be happy to let someone sit there and quietly watch me do what I see as necessary, as the "expert".

If you want to expand your knowledge of tube amps, start by reading up on the basics/safe practices & try a few simple amp mods/upgrades to develop your sense of how the whole thing works, rather than potentially draw out the tech time involved in servicing your amp. Techs are not getting rich off servicing Princetons, if he is busy, he will need to work at a reasonable speed. There's a difference between actual hours spent on a service & subsequent checks, as opposed to chargeable hours.

Not trying to sound pompous here, you value your amp and want to be sure that it's getting the proper care...but you wouldn't expect to sit in on a relatives surgery, quizzing the surgeon, in a bid to learn more about anatomy, or insist on watching your meal being cooked in a restaurant?

[Enzo]

Amen. I wouldn;t send instruction to the restaurant kitchen to make sure the cuting boards were clean, check for pieces of egg shell in my omelet, don;t use sugar in pkace of salt, etc. I expect them to be competent. Your amp tech knows to check for noisy controls, loose jacks, bias levels, etc.


By the way, make sure your guitar is tuned before you play, and check for loose strap buttons.

[MikeJr.]

An excellent point....

MJWB & Enzo,

Your point is well taken. I can be flexible on this! Good list MJWB.

Pontiacpete, As I look into this I am confused as my 20 inch amp will take a 17" reverb tank which looks like type 4 (two spring) vs the type 8 which is shorter with three springs. Are you sure your original recommendation of the accutronics 4AG3CIB is not the correct one? Is this an issue I should leave to a tech to help me decipher? Accutronics has a useful identification page at Accutronics Reverb by Sound Enhancement Products, Inc.. There are definately a few numbers in the middle of the specification chart which are foreign to me. Maybe my stock reverb tank has a production code???

Take care,

Mike

[MWJB]

The stock Fender tank is 16.7", 4AB3C1B is the stock tank, your tank should have a number stamped on to it. 9AB2C1B is the comparable, 16.7", 3 spring tank.

[pontiacpete]

post #8

I corrected myself in post #8
the reverb in my SF princeton is here

Accutronics 8AB2A1B Reverb Tank. Its sold at tubedepot.com for the following price(don't know where the link is, try post #8)

this is an 8" tank with 3 springs for $24.95 + $4.95 shipping.
It is an equivalent to the 4AB3C1B but shorter.

If I were you I would put that in myself and save a few dollars. Heck, I've had techs on 2 different occasions put the wrong tank in.

pete