issue with '72 Deluxe Reverb

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Stevie, Aug 7, 2011.

  1. Stevie

    Stevie Member

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    http://photoshare.shaw.ca/messages/viewimage/18709562600-1311660943-24043/parm/22231357/page/1/15

    Hi folks!

    I have a '72 SFDR that doesn't sound so good at this time (to my ears anyways). It's 39 years old and started sounding "tired" so I had a cap job done and "blackfaced". That didn't really improve the sound any so I changed all the tubes (tried new tubes and NOS tubes)...not much difference in sound. Changed the speaker (tried a Cannabis Rex and Weber 12F150 25W)...a little better but still sounds muffled and mid-range and honky. The bass doesn't seem to do much and the treble is very dominant so I removed one side of the bright cap which tamed it some but even now the treble at 4 is still dominating which causes the amp to sound thin and brittle and honky...did I mention honky?

    I'm debating replacing ALL the caps on the turret board with new Sozo caps since I want to check them all out anyways. It wouldn't take too long to just replace as lifting one side to measure them. The amp has the "blue turds" which I understand don't usually go bad so should I change them or not?

    I wonder if the iron could be breaking down and needing replacing. How could I easily confirm if the transformers (PO and OT, choke) are bad?

    If I'm going to replace all the caps on the board, which caps do you recommend? I was considering standard sozo or the new sozo blue molded caps. Anyone have any experience with these?

    The half-dozen resistors I checked are all within spec so I don't think I need to worry about those...or do I?

    Any help/advice would be greatly appreciated.
     
    Last edited: Aug 8, 2011
  2. tmac

    tmac Goldmember Silver Supporting Member

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    pics don't show a cap job.
    generally you should check or just go ahead & replace all the white electrolytic caps on the main board. No need to replace the blue coupling caps unless they're leaky, those are good sounding caps, the brown "turds" are the ones w/the bad rap (and those aren't even as bad as people say IMO, I've heard some great sounding amps with those in 'em).

    If u haven't done already replace the bias cap, and power supply caps in the doghouse. Unless something else is amiss that's generally what would be needed.
     
  3. Tuberattler

    Tuberattler Member

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    Don't replace the blue turds unless they are bad, as they sound good, the white caps are usually good too. A total board cap job is not usually the suspect in this scenario. I agree with tmac on the bias cap and all the e-caps in the under chassis doghouse. This should give you back the richness and warmth of these amps.
     
  4. phsyconoodler

    phsyconoodler Member

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    Those white bypass caps on the main board can cause issues.Replace them and see if that helps.
    Check the resistor that runs from the left lug of the bass pot to ground.That sets the amount of mids because the Deluxe doesn't have a mid control.If it's drifted a lot it will be a real issue.
    I agree with the previous answers for sure.ALL the electrolytic capacitors need to be changed.
     
  5. smolder

    smolder Gold Supporting Member

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    Which is NOT to say that ALL capacitors need to be changed.
     
  6. phsyconoodler

    phsyconoodler Member

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    Big emphasis on "ELECTROLYTIC"
     
  7. Marshamps

    Marshamps Member

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    If the cap job was done recently (and correctly), and the Blue Turds are not not leaking Voltage, It could be your OT. A replacement Heyboer or Mercury would be a good choice.
     
  8. phsyconoodler

    phsyconoodler Member

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  9. Stevie

    Stevie Member

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    Well I brought the amp to my friend, Mark Stephenson from Stephenson Amps ( http://www.stephensonamps.com ). Several caps were leaking and a few resistors had drifted, a couple of cold solder joints, better filter caps and PRESTO, the amp sounds fantastic. Now to find a 12" Celestion Gold speaker...

    I was considering moving the amp but now it sounds so good, it's a keeper! I'll post a picture of innards a little later this evening.

    Thanks for your advice
     
  10. smolder

    smolder Gold Supporting Member

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    don't ya hate it when that happens? ; )
     
  11. Tuberattler

    Tuberattler Member

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    Sweet I like it when a plan comes together!! Congrats! enjoy :)
     
  12. Stevie

    Stevie Member

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  13. phsyconoodler

    phsyconoodler Member

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    Quote:" Now to find a 12" Celestion Gold speaker..."

    No,no,no!!!!

    They sound rather thin in a Deluxe Reverb.A Weber 12F150 is what you need.

    The 'after' pictures still show the same old white bypass caps but new filter caps(good) So it's still not 'fully' serviced.But if you are happy with it,then you are still way ahead.I don't see where he changed any resistors?? The cap hanging off the bias pot reeks of the old silver-face bias balance system.He should have changed it to a bias-'balance' so you can actually change the bias when you install new power tubes.As it is you pop in tubes,turn the balance pot to minimum hum and 'hope' they draw the right current.
     
  14. Stevie

    Stevie Member

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    there are a couple of old caps left, yes. I don't use the normal channel so it was left as is as the tone caps are good. The two other white caps were not leaking and read the correct value. On the Vibrato channel Mark put in a couple of vintage Astron Blue caps and a silver mica cap. The Bias is a balanced bias, the bias pot affects current in both tubes not just the one.

    I just took out a 12F150 as I found it bright sounding (it is new mind you) but I believe any speaker should have a basic sound that should improve with use and find the Weber was just too bright. I may try a Cannabis-Rex again...heck maybe even a Jensen C12K as I found it sounding good in the DRRI amps and wonder how it would sound in this amp.
     
  15. phsyconoodler

    phsyconoodler Member

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    Quote:"The two other white caps were not leaking and read the correct value."
    Maybe,but they are electrolytic and should be changed.

    Weber 12F150 trebly?Hmm....was that tested when your amp wasn't sounding right or after it was serviced?
    Jensen C12K will sound killer good.You might like the Celestion Gold but I find them to have too much high-end and mids.Better in a Vox.

    The normal channel affects the reverb channel even though you don't use it.There is a shared cathode bypass cap and resistor and even changing the tube in V1 to a different one will have some effect on the tone of the reverb channel.Slight sometimes and more other times depending on the amount of gain the tube has.Try this:remove V1 altogether.You will have a bit more punch on the reverb channel.
     
  16. TheAmpNerd

    TheAmpNerd Member

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    Hi Guys,

    I would make sure to change out the white electrolytic in the
    trem circuit. I've seen more than a few of these blow up in an amp.

    The are a real mess to clean up too.

    Have fun and make music.
     
  17. JJman

    JJman Member

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    I've read that the original white (Mallory) preamp cathode bypass caps are actually not electrolytic. I changed them in my '71 DR and '74 VC. I keep all vintage parts and I just tested a 25u. It's showing 26.5u.
     

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