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My 73 Fender Deluxe Reverb Silverface Repair

Discussion in 'Amp Tech Center' started by Distractor_Beam, May 6, 2020.

  1. Distractor_Beam

    Distractor_Beam TDPRI Member

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    I had a 73 Fender Deluxe Reverb Silverface with scratching, humming, and mostly popping noises coming from it.

    I did a repair including:

    Replacing the rectifier and power tubes
    Replacing the negative bias cap
    Replacing the filter caps
    Replacing the main grid caps
    Biasing it
    Replacing the vibrato speed pot and knob

    I don't know if it'll help anyone around here, but if anyone's interested, I made a video:



     
  2. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Nice first post. Welcome to TDPRI.

    Congratulations on getting it to sound good again. It is a lot of work to make a "how to" video.

    Hope you don't mind a Nit Pik... I would like to have seen a better representation of caution concerning the high voltages. You mentioned/showed checking them. I think the viewing audience varies from novice to professional, and a novice may not know the gravity of a mishap.

    Again welcome. I appreciate your talent. Nice job!
     
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  3. Wally

    Wally Telefied Ad Free Member

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    One question...what is a ‘main grid cap’? I’ll have to find the t8me to watch the video. Welcome to the forum.
     
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  4. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    Welcome!

    Curious as to why you replaced these tubes. Unless voltages were wonky (after factoring the specified voltages for modern wall voltage of 119-121VAC) Those tubes generally last for 50 or 60 years - they're usually GE or RCA tubes. On those RCA's a the scorch marks rarely mean anything - if the bias OK and sound good they could last another 25 years...but I didn't notice you checking the bias on the ORIGINAL tubes, which are inherently better quality than new Russian Mullards.

    They and the power tubes can't be tested on a common Hickok BK or other vintage tube tester, even if calibrated (which has to be done every 5 years) - the plate voltages max out at 185. You have to have a very expensive, rare, military tester with high voltage (and calibrated) or a new Orange or custom-built tester to test power and rectifier tubes.

    Same deal with power tubes - if they were original and bias to within 5 ma or so of each other they don't require replacement unless the audio issues were isolated to the power section - and you'd pretty much need a 'scope to do that.

    Please don't take this as criticism - it's just that many newbies read posts like yours and think they need to do wholesale replacement of parts when it's unnecessary. So I am just hoping you can expand on your reasoning and what the needs were for those replacements.

    Also, as far as biasing goes - math has no tone. You did a sound test, but the only really valid sound test is with the owner playing - with HIS guitar. It only takes a few minutes and you get a true "reality check".

    So after figuring a "safe zone" dissipation-wise I run the amp with the player cranking away at HIS volume level, attack etc. It's the only way to know if the bias is OK or not - tweaking it a few ma each way for tone. Granted, not everyone takes the time to do it that way - but it makes for happier customers and virtually zero "bring back for adjustments".

    And FWIW - Sprague Atoms are not the same quality as the Atoms we could buy 10-15 years ago. When they were bought out by an overseas company they cheapened the construction - using the same big blue can, but stuffed with small Chinese "guts". Pictures were posted by several members a few years ago of new caps cut in half.

    They're also the most expensive common caps and IMO a waste of money.

    Common subs for bias caps are 100uf/100V. That's what we stock around here an d install in virtually every Fender BF/SF amp. Almost everyone makes them the same size as the old Mallorys, selling at $2-4 each

    Most of us around L.A. simply refuse to install Atoms anywhere.

    Hope that's helpful - and again, welcome to the board!

    Also - why did you replace the PI caps? Did they test bad with your LTE meter (I'm assuming you have one to test caps - I didn't see one)?
     
    Last edited: May 7, 2020
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  5. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    I'm guessing the 470 or 1500 ohm resistor. not cap. Since many amps don't have the 470's probably the 1500's, which are "stock".

    I need to watch the video as well - I just rarely have the time to watch all the videos posted - 5 minute ones, yes - but 45 minutes never.

    I jumped around the video - never did figure the "main grid cap" out.
     
    Last edited: May 7, 2020
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  6. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Sounds like a good normal general service to me!
     
  7. Wally

    Wally Telefied Ad Free Member

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    Okay....so screen grid caps on the power tubes. I simply have never heard or read the phrase ‘main grid’. Control grid, screen grid, suppressor grid.....those are the terms for grids with which I am familiar.
     
  8. Distractor_Beam

    Distractor_Beam TDPRI Member

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    Hey guys, thanks for the interest. I've played around with electronics for years, but this was my first time with a vintage amp. I have plenty of catching up to do.

    You are right about that. I often have difficulty with deciding how much information to include. In retrospect, I also feel like that should've been included.

    I called it the main grid cap, I meant to say grid coupling cap, which is what I had heard it referred to as. Screen grid, as you put it, sounds like the better term, and I'll refer to it that way in the future.

    I don't have an LTE meter, and I don't really know what that is. Is that the same as an ESR meter? I replaced those caps because I was mainly concerned about the age, and I'd come across a horror story about when they went bad, they fried the tubes. I had 2 goals with this job, the first was to clean up the sound, and the 2nd was preventative maintenance. I really wanted to keep as much of the original amp as I possibly could, but I also wanted to make sure that it's not going to burn up any time in the near future.

    I still have them, and one day I may put them back in to see if the sound problems come back. The main reason I replaced them is that the research I did lead me to believe that most of the time, when getting audio issues, it's tube related. Before I did any work on the amp, the first thing I did was tap on the tubes, and the only one I got any feedback from was the rectifier. My first thought was that it was the socket, and I actually got a replacement for it, but when I put these tubes in and I didn't have any issues, I left that alone. After pulling them out, and seeing the scorch marks, that sent up a red flag for me, so that's when I decided to cover my bases when I was doing the ordering. I hate to argue, but I believe that the Mullards are British.

    That's a great point. In the event I make a follow up, I'll definitely give you credit where credit is due.

    I agree that these are way overpriced. I saw the pictures of the chopped atom before I got it, and the main reason I still got it was that it was the exact uf as the original I was pulling out. I felt compelled to keep it as close to the original as absolutely possible.

    Again, thanks everyone for the feedback. I'm looking forward to more fun in the future.
     
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  9. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

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    They are distributed by New Sensor and made at the Reflektor factory in Russia. Only the originals were British. The specs are close but the construction and QC are not the same as that of the British Blackburn factory.

    New Sensor and a few other companies bought rights to names - like the Italian firm that purchased the "Jensen" name and makes speakers with the same part numbers as 1960's made in USA Jensens. But the performance is nowhere near the originals.

    I don't have any idea what horror stories you are talking about, and I've been doing this stuff since the 70's. Never had PI cap fail and damage a tube.

    Scorch marks are usually meaningless. Amps get hot and heat can cause discoloration unrelated to performance. If you were concerned about those power tubes the usual bench method (with no scope) is to check the plate voltage, then bias the tubes to roughly 70% dissipation. If they bias to within 5ma of each other they're fine - 7-8 ma can be OK if the amp sounds OK. But you don't start discarding power tubes without having checked the bias - and even then, if the bias is spread is 0-7 you need to check the entire PI first to make sure IT'S balanced or if you have issues in a gain stage.

    A tapped rectifier tube that makes noise isn't due to the tube - it's not in the audio path. There was no reason to replace it at that point. It sounds like possibly a lead dress issue - a high-voltage wire from the rectifier resting against a wire or other part in the audio path. Move the wire so it's not touching - problem solved.

    Well - I don't know any amp techs who don't have an LCR meter. It's my #2 tool behind my Fluke Multimeter. An LCP Meter measures Capacitance and Equivalent Series Resistance in Capacitors; Inductance for testing coils (chokes, inductors etc; and Resistance (you don't have to switch to your multimeter when checking capacitance and resistance).

    It tells you if a cap is on-spec in microfarads and the ESR level. The only physical test for caps is recognizing if one is leaking fluid - but most "off spec" caps aren't leaking fluid. The ESR is heading for the stratosphere long before the cap physically goes "poof" along with the power transformer.

    You don't have any way to know if the capacitance is correct without an LCR meter, and replacing caps based on isolated internet rumors is a waste of time and money - and often downgrades the value of the amp.

    In the 80's and 90's many "garage techs" discarded perfectly good blue tubular Ajax caps in the PI, tone circuit, coupling caps - because the caps were old and they heard the amp needed a "cap job" through reading a Gerald Weber book - so they replaced 'em with orange drops...and Wally, me and several others tore our hair out because we would have BOUGHT those caps!!

    Just a few things to think about in the future.
     
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  10. Distractor_Beam

    Distractor_Beam TDPRI Member

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    This is interesting. I've never even heard of an LCR meter. What's your go to brand or model?

    You're proving to be absolutely full of useful information. Had it not been for you I'd be bragging about my fancy British tubes like someone bragging about their American made Ford or Dodge vehicle.

    Thank you very much.
     
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