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Thread: Volume issue with Fender Tweed Princeton

  1. #1
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    Volume issue with Fender Tweed Princeton

    Hi,
    This amp's volume works up to about 5 then levels back down to 4 for the rest of the pots turn to 10. If that makes sense. The middle is loud as it gets and then it slightly goes down in volume and holds that volume to 10 on the dial.

    I have replaced the pot twice (1M-A), (1M-B just to make sure), swapped out the 12ax7, and checked out the resistors (they seem to read within 10% of the values. I have a bit higher voltage than what the layout says should be present. Could that cause this volume pot issue?

    I have been looking at the schematic and can not figure out the issue yet.

    I have been reading about screen resistors on the 6v6. I am going to try to find a different 6v6 to swap out tomorrow to see if that helps. The volume is not cutting out, it just stays at the same level.



    Any suggestions?



    Amp Guide Fender*Princeton (Wide Panel)

  2. #2
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    It's got nothing to do with your voltages.

    Can you post a pic of what you have done (not a schem, not a link to the Fender schem/layout)?

    "I have been looking at the schematic and can not figure out the issue yet." That's probably because the amps based on the schematic worked properly, we need to establish whether you have actually built the amp as per the schematic.

    Did you try pots of different brands, rather than just different tapers?

  3. #3
    Old Timer Amp Kat's Avatar
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    Does it have reverb and what happens if you disconnect or turn the reverb off ?
    KB

  4. #4
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    Here is a picture of the OT that was in the amp.
    Attached Thumbnails Attached Thumbnails fender-princeton-ot.jpg  

  5. #5
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    Here is a picture of the insides with the OT removed. This amp was a beater and I also had to replace the PT.

    I did try different brands with the pot changes. I also tried swapping around 6V6's today without any luck. I am guessing the OT at this point. Is there a simple way to test it outside of the amp with an Ohm meter? And if so what points should read what reading?

    Thanks,
    Attached Thumbnails Attached Thumbnails 5d2-guts.jpg  

  6. #6
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    I can post closer pictures of the wiring if needed.

  7. #7
    Senior Member Enzo's Avatar
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    The OT has no idea where teh volume control is set, it isn;t the OT. Or if it is, it is a new one on me.


    Try it with the tone control max and then with tone at minimum. Does that change at all the way the volume control works?
    Education is what you're left with after you have forgotten what you have learned.

  8. #8
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    no, the tone control does not effect the volume.

  9. #9
    Senior Member JHow's Avatar
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    Do you have a good ground connection on the volume pot?

  10. #10
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    It is taking its ground from the metal body of the pot.

  11. #11
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    From some googling it seems the OT in this amp is a model 45-723 Calrad brand.

    Quoted from the Calrad website:

    45-721 or 45-721 L (5-70V) 45-723 or 45-723L (10-70V) 5 AND 10 WATT, 70 VOLT
    MATCHING LINE TRANSFORMERS
    (SPECIFY WITH OR WITHOUT LEADS)
    Universal 70 volt 5 & 10 watt audio line transformer for chassis or speaker mounting, can be connected to an audio amplifier to enable proper line and speaker impedance. Matches 4 to 8 ohm speakers. Taps of 0.31, 0.62, 1.25, 2.5, 5 watts for the 45-721. Taps of 0.625, 1.25, 2.5. 5, 10 watts for the 45-723.

  12. #12
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    After taking off the OT and putting it back, I am now getting very low volume across the entire pot.
    Last edited by delayed; 06-24-2010 at 07:58 AM.

  13. #13
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    None of the specs on that OT mean diddley to me, it's not the original OT, buy a heavy duty Champ style replacement OT.

    You could measure the resistance between the primaries on the Calrad (200-400ohms maybe?)...but that won't tell you what the primary Z is, or whether you have a good speaker match. Ideally you want to apply a low voltage AC source to the secondaries (0.5VAC to perhaps 6.3VAC) then divide the voltage developed accross the primaries by the secondary voltage, square the result & multiply by speaker load to determine primary Z, e.g.:

    Apply 0.5VAC at the secondaries & you see 18.5v at the primary (use 2 voltmeters, one on the primary, one on the secondary)...

    18.5/0.5 = 37v

    37*37 = 1369

    1369*4ohms (speaker load) = 5476ohms primary Z...a champ style OT might read from this up to 8K.

  14. #14
    Old Timer Amp Kat's Avatar
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    Whoa there buddy that is not a tube OT but a SS 70 volt tranny for PA distribution speakers like you see in the Wal-Mart or by Executone. You need a real tube output transformer from Mojo or other Guitar amp distribution like Mercury Magnetics.
    KB

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    Thank you for the information. It is really helpful. I figured this was the incorrect type for the application, but was not for sure. I will mess around with applying some voltage to it to learn a bit more about transformers.

    Does anyone have any suggestions on a certain model to get?
    Here are a few that I think should work,


    OT FTPO-55 '55 Tweed 85.00 From:
    Mercury Magnetics -- The Guitar Amp Transformer Company

    TF103-48 Single Ended Champ Transormer with 4/8 Ohm Output
    TF103-48$19.95 From:
    TF103-48 Single Ended Champ Transformer with 4/8 Ohm Output

    Tweed Champ Style NOS Output Transformer
    Item Number: NOS771 $30.00 From:
    Mojo Transformers Tweed Champ Style NOS Output Transformer

  16. #16
    Senior Member JHow's Avatar
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    Also Weber has what I would call a replica ($25) version (and they carry Heyboer and Merc Mag too):

    https://taweber.powweb.com/store/022905sch.jpg

  17. #17
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    Buy the one with the highest W rating & dc current rating, tweed princetons are hard on the OTs. Interesting to note that Weber do not supply the 022905 OT with their 5F2A kit, they use the P-P princeton OT instead.

  18. #18
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    I made an order for an OT. It ships Monday, so maybe by Thursday I will know if this fixes the problem. Thanks for all the replies.

  19. #19
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    The OT came in and it did not fix the volume issue. Changing the .02 caps did. Both tested to .02 but one reading 15 ohms and the other started at 400k and slowly went up to the MegOhm point. Swapped them out and all is fine sounding now.

    Does that mean it was passing DC?

    The new OT transformer sounds fine to me. I went with the 20 dollar one from Triode Electronics Inc. They shipped quickly and when promised.

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