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  1. Replies
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    I just repaired a K250-4, it had a lot of hiss....

    I just repaired a K250-4, it had a lot of hiss. Bad opamp caused it. Luckily it was a 4558 so easily replaceable.

    These will normally have a certain amount of hiss, but the older technology opamps...
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    212

    Plug the guitar into the in of one Y-cord. ...

    Plug the guitar into the in of one Y-cord.

    Feed one Y output directly to the amp, feed the other Y output to the input of the RM.

    Put the volume pedal inline with the output of the RM going...
  3. If there are silpads on the originals, I will...

    If there are silpads on the originals, I will inspect and reuse when possible. When the insulators must be replaced, I just use mica and Wakefield silicon grease.
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    354

    Earlier on you posted that the input transistors...

    Earlier on you posted that the input transistors were 2SB54's. Can you use one of those for the driver position and replace the input with another less critical one?
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    Have to agree with nickb above. If the basic...

    Have to agree with nickb above. If the basic first recording is weak there will be very little regenerated echoes.

    Of the ones that I have repaired, the tape cartridge was the usual place to solve...
  6. On the original transformers, there is no center...

    On the original transformers, there is no center tap on the HV secondary. They use a full wave bridge to get the final dc voltage.

    Normally there are 4 diodes in the high voltage power supply...
  7. As a follow up, the UTC "ouncer" model O-1 would...

    As a follow up, the UTC "ouncer" model O-1 would seem to fit the bill.

    There are a number of 1970's UTC catalogs scanned and online out there. Who knew?
  8. What ac voltages are you getting directly from...

    What ac voltages are you getting directly from the power transformer?
  9. Replies
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    150

    Interesting, I have not seen that style of trem...

    Interesting, I have not seen that style of trem before. Instead of varying output bias or shunting audio signal to ground, they are basically shunting the two input grids of the power tubes together....
  10. Looking at the photo of the original...

    Looking at the photo of the original switch/transformer assembly, that looks like a UTC matching transformer. United Transformer Corp, New York.

    If there are other photos available, there will be...
  11. Perhaps if you look at it this way, -16.4 less...

    Perhaps if you look at it this way, -16.4 less 0.7 equals -15.7.
  12. Replies
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    Thanks for posting the schematic. That's quite...

    Thanks for posting the schematic.

    That's quite an amp, dc preamp filaments, 6V6 drive to the reverb tank.
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    Just as a point of reference, I just fixed an...

    Just as a point of reference, I just fixed an original 1969 Fender Telecaster. The pots were both 1 Meg Audio and the volume pot had a 0.001 bleeder cap.
  14. Replies
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    When I was a kid my dad told me to tap the tube...

    When I was a kid my dad told me to tap the tube while holding the test button down. Sometimes the short light will go on and off and sometimes it will come on and stay on.

    Sometimes when there is...
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    555

    I assume that you mean if you shake the tank the...

    I assume that you mean if you shake the tank the springs you can hear them through through the speakers? The reverb return circuit is done with opamps, the drive circuit is part of the 15 vdc...
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    555

    This is a single sided power supply for the...

    This is a single sided power supply for the opamps, so there should be 30 vdc on pin 8 and ground 0 volts on pin 4. So the reading you get at IC1 are correct, with about 15 volts bias on all of the...
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    220

    If there is hiss coming from the speaker, you can...

    If there is hiss coming from the speaker, you can probably rule out an output transformer or power tube problem. Have you checked the tubes?

    Visually check all of the solder joints on the tube...
  18. The small second transformer is an isolation...

    The small second transformer is an isolation transformer that separates the ac line ground from the input audio ground. So in theory the input ground is already ac isolated.

    In normal...
  19. Replies
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    1,005

    Build yourself a light bulb limiter and use it...

    Build yourself a light bulb limiter and use it during start up tests. It might save you a bunch of new parts if you don't catch all of the shorted ones.
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    Welcome to the place. It might help us all to...

    Welcome to the place.

    It might help us all to know what amp you are talking about and maybe a link to an owner's manual.
  21. Welcome to the place. While I don't care one...

    Welcome to the place.

    While I don't care one way or the other, you might want to start a new thread for your amp so we don't start to get things confused with the earlier one.

    Do you have an...
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    When the filter cap cans were replaced was the...

    When the filter cap cans were replaced was the original grounding scheme followed? Ampegs will hum from ground loops if the cans are not grounded correctly.
  23. Replies
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    If the return circuit is not working, there will...

    If the return circuit is not working, there will not be any reverb. Start by checking the return circuit transistor and input cap.

    You can take the reverb tank output and send it to another amp...
  24. Do you have a multimeter that can test diodes? ...

    Do you have a multimeter that can test diodes?

    The burnt yellow cap next to the power jack is definitely a tantalum cap, so get one like they told you, to replace it. The board will probably be...
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    They are supposed to hold the footswitch. You...

    They are supposed to hold the footswitch. You slide the footswitch between the two plastic extrusions. The back panel has a little notch cut out so that the footswitch will slide under the cross...
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    Agree, 100% about Austin at ZT. Very helpful and...

    Agree, 100% about Austin at ZT. Very helpful and open about troubleshooting his product.

    One thing that I didn't like was the rubber cement like coating poured over the input jack and other...
  27. The Master Volume on this amp should effect the...

    The Master Volume on this amp should effect the volume of both channels. If it has failed both channels would be quiet not just the vibrato channel. Crackling usually only happens when a control is...
  28. Replies
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    Did you do the recap on this amp? My guess is...

    Did you do the recap on this amp?

    My guess is that the problem lies in either the Q205 circuit or the modulator circuit. Have you tested all of the diodes in the ring and oscillator? The fact that...
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