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Thread: Princeton slow warm-up

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    Princeton slow warm-up

    I have a '71 Princeton Reverb that takes about twice as long to warm up as other tube amps I've used. First off, what might cause this? And secondly, is it something to worry about? All the tubes checked out fine, if that could have been an issue.

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    Re: Princeton slow warm-up

    I don't think it's anything to worry about necessarily. What type of rectifier tube is it using? How old are the power supply capacitors?

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    Re: Princeton slow warm-up

    5U4 rectifier tube. It had been suffering from a bad socket, but socket is replaced and works fine now. Tube is good. I don't know about the caps. Probably original. I got the amp used 25 - 30 years ago. I know the speaker was replaced (Eminence 12" now), and I really liked its sound. Other than that I don't know any of its history. It's mostly been in storage since then (yeah, I had one of those "never at home" jobs), so I've used it very little. I'm just trying to get everything back up and running now that I'm finally retired and didn't know if this was an issue that needed attention or not.

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    Re: Princeton slow warm-up

    If the electrolytic caps are original, they're almost 50 years old and should be replaced. There are replacement cap "cans" available.

    If you're not electronically inclined, then try to find a qualified amp tech in your area.

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    Re: Princeton slow warm-up

    Quote Originally Posted by vinyl View Post
    If the electrolytic caps are original, they're almost 50 years old and should be replaced. There are replacement cap "cans" available.

    If you're not electronically inclined, then try to find a qualified amp tech in your area.
    Yeah, no doubt. Would that cause a slow warm up though? Are those old caps potentially causing some other damage?
    Thanks for the help so far.

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    Re: Princeton slow warm-up

    Merely suggesting a starting point. Since I'm not clairvoyant, I'll ask this: Is a slow warmup solely attributable to a rectifier tube?, power supply capacitors? loose or dirty tube sockets of other tubes?

    Since you have an amp that is almost 50 years old, could it be that it has additional issues that don't have anything to do with how long it takes to warm up? Leaky brown turd coupling caps?

    Would any of that possibly cause damage? In some cases, I say maybe yes. But then again, I'm not clairvoyant.

    Do you plan to keep the amp or just sell it for a little extra retirement cash?

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    Re: Princeton slow warm-up

    What vinyl said.

    Do the electrolytic capacitors and please do not forget the bias supply capacitor.

    Ps. We love pictures!
    What happend?
    Who let the magic smoke out?

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    Re: Princeton slow warm-up

    I plan to keep it. Like I said, I like the way it sounds (which is pretty much the point of it all, right? :) But if it's going to nickel and dime me to death it might be better just to get a new one (less cost in the long run). I can always swap the speaker out, because I'm sure that has a lot to do with the sound. It would be great to get a guitar tech to go through it, but they're pretty pricey these days (plus I have a bad track record for finding competent workers). Other than a slow warmup it works great and sounds great, so not sure if I'm making a problem where there is none. "If it ain't broke, don't fix it" sort of thing.

    I'm OK with a soldering gun. I put the new socket in, have cleaned all the other ones. It has a mixed bag of tubes - Mesa, RCA, etc... the secret concoction that gives it that magical tone! :) And I've seen kits online for all the capacitors, though I don't know if they are the same quality, or would effect the sound.

    As for photos, I don't think I'm allowed to yet. I just signed up yesterday and it indicated not.

    Again, thanks for the suggestions.

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    Re: Princeton slow warm-up

    How to post photos:
    https://www.thefenderforum.com/forum/showthread.php?51700-TUTORIAL-How-To-Post-Photos-on-TFF




    Back in 2014, I recapped a 1961 princeton that had been sitting in my garage since 1980. It didn't have a speaker. I haven't spent a dime on it since 2014, so I don't think you'll be "nickel and diming" yourself.

    The hardest part would be de-soldering the cap can from the chassis and soldering a new one in, if you don't have a soldering iron that gets hot enough. You mention a soldering gun, and that may be enough.

    Here's a couple of pics.




    I'm retired, and I get that you don't want to spend a boatload of money. But I believe replacing electrolytic capacitors won't affect tone. If I'm wrong, you can always swap the old shit back in. At your own risk.
    Last edited by vinyl; 09-01-2020 at 12:19 PM.

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    Re: Princeton slow warm-up

    So,
    I'm learning how edits work.

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    Forum Member Don's Avatar
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    Re: Princeton slow warm-up

    That's a beautiful amp and a huge soldering iron! My chassis soldering iron is an 100 watt Weller. It has about a 5/16" wide tip and just gets the job done.

    To the OP- I'm pretty conservative with electrolytic caps and replace them at around 20 years. Cap cans seem to last a long time, but 50 years is way too long. If you replace the electrolytic caps, any drifting coupling caps, resistors in the bias and power supplies, worn out jacks and tidy things up, these old amps won't nickel and dime you any more than a new tube amp will.

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    Re: Princeton slow warm-up

    Quote Originally Posted by Don View Post
    That's a beautiful amp and a huge soldering iron! My chassis soldering iron is an 100 watt Weller. It has about a 5/16" wide tip and just gets the job done.

    To the OP- I'm pretty conservative with electrolytic caps and replace them at around 20 years. Cap cans seem to last a long time, but 50 years is way too long. If you replace the electrolytic caps, any drifting coupling caps, resistors in the bias and power supplies, worn out jacks and tidy things up, these old amps won't nickel and dime you any more than a new tube amp will.
    Thanks, Don. That soldering iron belonged to my grandfather.
    But the point of my post is you can (and maybe should) replace certain components in old amps. I don't think it necessarily devalues them, or has much affect on how they sound.

    Cheers,
    vinyl

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    Forum Member Don's Avatar
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    Re: Princeton slow warm-up

    Quote Originally Posted by vinyl View Post
    Thanks, Don. That soldering iron belonged to my grandfather.
    But the point of my post is you can (and maybe should) replace certain components in old amps. I don't think it necessarily devalues them, or has much affect on how they sound.

    Cheers,
    vinyl
    You are correct!

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    Re: Princeton slow warm-up







    That took awhile to figure out. Sorry for the delayed response, I'm not the sharpest tool in the shed when it comes to computers. Anyhow, it looks pretty much original, except for that bare wire off the power plug. I'm guessing this was not a 3-prong plug to begin with and somebody in the past made it into one (whether right or wrong, I don't know)
    As for soldering irons, I have 25,35, 100, 200, and 400 watt models, so something in that lineup should work. On that electrolytic cap I'll have to take a closer look (as far as making sure it isn't holding any charge) as to which contacts to use to short it. Doubt it has anything in it at this point anyway. Haven't used it in quite awhile.

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    Re: Princeton slow warm-up

    Thanks for the pics, Sammich. Seems you are well equipped to replace the cap can, and all the other electrolytic caps in your amp.

    From your pics, all of the electrolytic caps appear to be original. They'll probably have date codes on them that begin with 235.

    So, for my point, if you replace those electrolytic caps you increase the longevity of your amp. If you do that, you probably won't spend another dime.

    I'm an old fart, and I don't expect any of my heirs will have any interest in my '61 Princeton. In the meantime, I'll enjoy it. Maybe they'll figure out that it has some value or not. Frankly I'd rather see it go to someone who appreciates what it is and would play through it and appreciates the history of Fender gear, rather than something that represents some monetary value.

    A vintage amp doesn't mean you will "nickel and dime" yourself to death. It just means you are a "custodian" of history until you pass it on to someone else.

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    Re: Princeton slow warm-up

    I agree with Vinyl. I'm not lucky enough to have snagged a vintage Fender, but I'd sure like to have a 59 Bassman and a 62 Strat.
    If we'd known we were going to be the Beatles, we'd have tried harder.--George Harrison

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    Re: Princeton slow warm-up

    Quote Originally Posted by ch willie View Post
    I agree with Vinyl. I'm not lucky enough to have snagged a vintage Fender, but I'd sure like to have a 59 Bassman and a 62 Strat.
    I'd just like to have the talent to play them!
    Striving to be ordinary

    Proud to be a TFF Dumbass!

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    Re: Princeton slow warm-up

    If I am not mistaken, some capacitors can hold a charge for many many months. I would always discharge them before working on the amp.
    "Live and learn and flip the burns"

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    Re: Princeton slow warm-up

    Quote Originally Posted by OldStrummer View Post
    I'd just like to have the talent to play them!
    I used to have the opinion that a player needs to "earn" a great instrument. But now I believe that if a guitar gives you joy, it doesn't matter if the only thing you can play is "House of the Rising Sun". Enjoyment leads to learning, and a 1st year player deserves a great guitar as much as any of us do. I seemed to get a guitar slightly better than the last as I developed as a guitarist, so I guess that's where my erroneous opinion came from. I started off playing pressboard pieces of crap.
    If we'd known we were going to be the Beatles, we'd have tried harder.--George Harrison

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    Re: Princeton slow warm-up

    So, I think we're digressing here. I'm probably just as guilty of that as anyone else.

    The main objective here is to help sammich with his amp. That is my main objective.

    Maybe I haven't achieved that goal, but that is what I'm trying to do.

    Sammich, I apologize. Threads can get derailed sometimes.

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    Re: Princeton slow warm-up

    I apologize for derailing. I just got excited about the talk of vintage amps. I appreciate you pointing it out, vinyl. No sarcasm intended.
    If we'd known we were going to be the Beatles, we'd have tried harder.--George Harrison

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    Forum Member Don's Avatar
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    Re: Princeton slow warm-up

    Along with all of the electrolytics, I also recommend that you replace the power supply resistors (the two large ones on the right end of the board in your third pic and the one on the cap can) with properly rated flame proof resistors. Replacing the bias supply resistor is good preventative maintenance as well.

    I can't see where the ground wire on the power cord is connected. It should be longer than the hot and neutral wires and have its own connection to the chassis (not connected to a transformer bolt).

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    Re: Princeton slow warm-up

    OK, so now I'm starting to wonder if I'm in too deep (this is where my eyes start to glaze over!). We started with the one cap can, and thanks for telling me the location of those three resistors (I'm good when someone points at something and says "do that"), but now it sounds like ALL the capacitors should be replaced? Isn't the bias resistor the one you already mentioned? And I didn't know resistors were rated as far as flammability goes.

    It looks like the ground wire off the power cord connects to the ground screw on the back of the auxiliary plug socket (which is a three prong). Are you cringing yet? :) I assume I need to drill a hole in the chassis and connect it directly.

    My electrical experience was mostly putting Heathkit and Radio Shack stuff together back in the '60s and '70s (like ham radios, etc). I did take amplifier classes in the '90s, but that was all theory, nothing hands on or about the actual guts. So, enough education and experience to be dangerous, but not enough to be knowledgeable and competent. That's what you're dealing with when I ask my questions (FYI).

    And no problem on the derailment. I was just reading along enjoying the stories.

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    Re: Princeton slow warm-up

    Quote Originally Posted by sammich View Post
    OK, so now I'm starting to wonder if I'm in too deep (this is where my eyes start to glaze over!). We started with the one cap can, and thanks for telling me the location of those three resistors (I'm good when someone points at something and says "do that"), but now it sounds like ALL the capacitors should be replaced? Isn't the bias resistor the one you already mentioned? And I didn't know resistors were rated as far as flammability goes.

    It looks like the ground wire off the power cord connects to the ground screw on the back of the auxiliary plug socket (which is a three prong). Are you cringing yet? :) I assume I need to drill a hole in the chassis and connect it directly.

    My electrical experience was mostly putting Heathkit and Radio Shack stuff together back in the '60s and '70s (like ham radios, etc). I did take amplifier classes in the '90s, but that was all theory, nothing hands on or about the actual guts. So, enough education and experience to be dangerous, but not enough to be knowledgeable and competent. That's what you're dealing with when I ask my questions (FYI).

    And no problem on the derailment. I was just reading along enjoying the stories.
    No drilling required!

    Ask any and all questions necessary to make you feel comfortable. There are no stupid questions.

    So, I have a few questions of my own. Do you have a VOM? (Volt Ohm Meter) Do you understand how to use it? If you look at a schematic, do you understand what the symbols mean? In other words, can you tell the difference between a resistor, capacitor, a transformer etc.?

    I would start with the electrolytic capacitors. That means the cap can, cathode bypass capacitors and the bias supply capacitor. That's a total of 8 capacitors. The cap can, 6 cathode bypass capacitors and 1 bias supply capacitor.
    Cheers,

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    Re: Princeton slow warm-up

    Yep, have a VOM and use it often for voltage and continuity checks (or actual ohms for something like guitar pickups :). I do fine reading schematics, though I don't have one for this amp. (no doubt Google can solve that problem)

    As far as that ground wire -- is it fine just hooked to the ground post on that plug socket?

    And then you lost me. I recognize the cap can, but not which ones are bypass caps or a single bias cap. But where you say 8 are present, I see 9 (the blue ones + the can, or am I looking at the wrong stuff?)
    (slight change of subject, but speaking of bias, I think this amp has auto-biasing, doesn't it?)

    Thanks for walking me through it, Vinyl

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    Re: Princeton slow warm-up

    Cathode bypass caps outlined in red. Bias supply cap outlined in green.



    I didn't outline the cap can. I assume you understant where that is.

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    Re: Princeton slow warm-up

    The bias supply cap deserves special attention to the polarity. The positive side of the cap goes to ground. All of the others, the negative side goes to ground.

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    Re: Princeton slow warm-up

    Wow, not even close, was I. This picture is definitely worth a thousand words with your boxes around the right caps. Thank you so much, Vinyl.
    I'll see if the local electronics store here has those (yep, we still have one of those - a dying breed). Or do you recommend any particular internet sites to order these?

    I saw that Don recommended replacing the power supply resistors and the bias supply resistor as well. I see two on the bias cap. Is that what's being referred to as far as the bias supply resistor goes? If so, which one, or both? (I didn't know resistors even wore out)

    In general (and to educate me), I often read that old amps need to be re-capped. Why is that? Do the caps not store a charge correctly anymore? Does something else get ruined in the amp if it has old / bad caps?

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    Re: Princeton slow warm-up

    Quote Originally Posted by sammich View Post
    Wow, not even close, was I. This picture is definitely worth a thousand words with your boxes around the right caps. Thank you so much, Vinyl.
    I'll see if the local electronics store here has those (yep, we still have one of those - a dying breed). Or do you recommend any particular internet sites to order these?

    I saw that Don recommended replacing the power supply resistors and the bias supply resistor as well. I see two on the bias cap. Is that what's being referred to as far as the bias supply resistor goes? If so, which one, or both? (I didn't know resistors even wore out)

    In general (and to educate me), I often read that old amps need to be re-capped. Why is that? Do the caps not store a charge correctly anymore? Does something else get ruined in the amp if it has old / bad caps?
    So I'll attempt to answer your questions.

    Https:www.tubesandmore.com will have the caps you need. They are currently having a labor day sale. I've used them in the past.

    If it were me, I'd use 25uF 50V Spragues for the cathode bypass caps, and a 100uF 100V F&T cap for the bias supply cap.

    Electronic components can "drift" in value over time. As far as electrolytic caps, you can search "Why do electrolytic caps require replacing in old equipment?"

    As far as resistors go, carbon comp resistors can drift in value too, but they're easy to check with a meter. Replacing them won't affect tone, just make sure you use the correct wattage.

    Lastly, the ground (green) wire on the power cord is probably fine where it is as long as the accessory outlet is tightly fastened to the chassis. Easily checked with a meter. There are other ways to change it without drilling any holes.

    There are a number of people here that can help you, I'm not the only one. The only reason I say that is I may have to make a trip somewhere soon and that may make it more difficult for me to reply.

    Cheers,

  30. #30
    Forum Member Don's Avatar
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    Re: Princeton slow warm-up

    Quote Originally Posted by sammich View Post
    I saw that Don recommended replacing the power supply resistors and the bias supply resistor as well. I see two on the bias cap. Is that what's being referred to as far as the bias supply resistor goes? If so, which one, or both? (I didn't know resistors even wore out)
    As vinyl said, components drift over time. Replacing the power supply and bias supply resistors, even if they haven't drifted much or failed, is about making the amp reliable. It's optional. I've seen them fail often enough that I recommend replacing them.

    Vinyl's recommendation on parts is right on. Sprague and F&T are great and that website is my go to for parts that I can't get at Mouser (like F&T caps and can caps).

    Here's a link to 2 watt resistors suitable for the power supply. There's a 1k ohm and an 18k ohm at the end of the main board and an 18k ohm on the can cap. Your local supplier should have similar resistors for even less money.

    https://www.tubesandmore.com/product...al-oxide-power

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    Re: Princeton slow warm-up

    Don and Vinyl - you both have been a tremendous help, and I think I've gotten almost all the answers I need. All that's left is getting the parts and doing the labor.

    One last thing, though. I'm still unclear on which resistor is the bias supply one. There are two connected to the bias capacitor (in parallel). Are those the ones? Or is it some other place entirely?

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    Re: Princeton slow warm-up

    And almost forgot - why are you recommending higher voltage caps than the originals?

  33. #33
    Forum Member Don's Avatar
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    Re: Princeton slow warm-up

    Quote Originally Posted by sammich View Post
    Don and Vinyl - you both have been a tremendous help, and I think I've gotten almost all the answers I need. All that's left is getting the parts and doing the labor.

    One last thing, though. I'm still unclear on which resistor is the bias supply one. There are two connected to the bias capacitor (in parallel). Are those the ones? Or is it some other place entirely?
    It's the 100k resistor on the bias board in series with the diode.

  34. #34
    Forum Member Don's Avatar
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    Re: Princeton slow warm-up

    Quote Originally Posted by sammich View Post
    And almost forgot - why are you recommending higher voltage caps than the originals?
    Wall voltages are higher than when these amps were built. There's nothing wrong with 25uF/25v caps for the cathode bypass caps, but I use 25uF/50v for other things and keep those on hand and use them wherever 25v or 50v is required. For the bias bypass cap, the voltage that the cap sees is closer to the 50v cap rating. 100v is better. Also, F&T offers a 100uF/100v and they're great caps. The only drawbacks to using high rated caps are price and size. If they fit, I use them.

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    Re: Princeton slow warm-up

    Thanks Don. I found schematics online (I think mine is the B1270, even though it looks just like the AA1164 [which I think is the earlier black face]). Anyhow, it showed the 100k resistor location and I finally saw it almost hidden under the bias cap (70v in this amp, so neither the 50v or 100v you and vinyl have mentioned).

    I also noted on the schematic that the resistor in parallel next to the bias cap should be a single 22k part. On my amp, though, there are two resistors wired in that position (values undetermined yet). Any comment on that?

    I've been trying to read up more on the different values for these parts, degradation of same, and get a little better idea of how it all works. It has turned out to be quite the rabbit hole. But, you and Vinyl have put me on the right track and helped a lot. Thanks.

  36. #36
    Forum Member Don's Avatar
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    Re: Princeton slow warm-up

    Quote Originally Posted by sammich View Post
    I also noted on the schematic that the resistor in parallel next to the bias cap should be a single 22k part. On my amp, though, there are two resistors wired in that position (values undetermined yet). Any comment on that?
    That resistor sets the bias. Does it look like someone added the extra resistor?

    Here's a website for some info-

    https://robrobinette.com/AA1164_Princeton_Reverb.htm

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    Re: Princeton slow warm-up

    Quote Originally Posted by Don View Post
    That resistor sets the bias. Does it look like someone added the extra resistor?

    Here's a website for some info-

    https://robrobinette.com/AA1164_Princeton_Reverb.htm
    Here's a picture. I can't tell if it was added or not. That's a good link you sent. Thanks. I'll study that some more



  38. #38
    Forum Member Don's Avatar
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    Re: Princeton slow warm-up

    That looks like a 100k and 28k resistor in parallel. That's 21,875 ohms. Close enough to the 22k that's on the schematic. Maybe they were out of 22k resistors that day?

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    Re: Princeton slow warm-up

    Quote Originally Posted by Don View Post
    That looks like a 100k and 28k resistor in parallel. That's 21,875 ohms. Close enough to the 22k that's on the schematic. Maybe they were out of 22k resistors that day?
    Could be. I'll have to talk to M. Torres (the name of the assembler shown on the chassis) about that! :)

    After going through that other link you sent me I noticed he recommended a different value phase inverter coupling capacitor to get rid of too much low end when a 12" speaker has replaced the stock 10" (which is the case with mine). I'll have to plug in and listen closely to see if this is something I'll want to try or not. I do like the sound of the 12", though.

    Anyhow, I think that's enough for now. thanks for all the help. We've taken quite a detour from the initial question about a slow warm-up.

    Adios

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