What do I have here?

Discussion in 'Shock Brother's DIY Amps' started by Ripdoozer, Dec 27, 2016.

  1. tubeswell

    tubeswell Friend of Leo's

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    You also may want to consider putting in a fresh rectifier tube and/or fitting 1000V 1A protection diodes in series between each HT winding end and each rectifier plate pin. This won't affect the performance of the amp or the rectifier, but will safeguard against the possibly of your old rectifier tube shorting out and taking out the filter caps (which they will with high VAC being dumped onto them) and thence taking out the PT. Adding extra SS diodes in series prevents this mode of failure, and is a no-brainer with vintage tube rectified amps
     
  2. Wally

    Wally Telefied Ad Free Member

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    Like I said....good luck with it all. 'Testing' that amp's AC votlage circuit in an unknown wall outlet is not a valid test, imho. One should know from looking at one's work whether or not the amp's AC input is correctly wired. (;^) There is no reason to test that, imho.
    Do you have a circuit outlet tester? They don't cost even $10....very valuable little piece of equipment for anyone who is interested in maintaining an existence on this plane. This will tell you about the wall outlet wiring.
    You might as well fire that amp up...dime the controls and wring it out for a few hours...just to make sure that it is going to be worth the expense of working on it, right????? (8^O
    "Two roads diverged in a yellow wood...." Again...my advice---which is worth about two cents....let that amp be until you recap it. More than likely, nothing bad will happen if you ignore this advice. However, if something catastrophically fail, don't say you were not warned. I err on the side of caution with these old things.....and have never lost a patient.
     
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  3. Ripdoozer

    Ripdoozer Tele-Meister

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    So, it looks like, in order to avoid I-told-you-so's by those who know more than me, I will take it to Mankato and have a trusted tech give it a checkup/overhaul. Probably be a month or more before I get to play through it.
    Maybe a smart decision, but not a very fun one.
     
  4. Wally

    Wally Telefied Ad Free Member

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    rip, like I said.....maybe you can play through it from now on and it will be fine. But....I had a BF Champ that I didn't do what I usually do....I let it be. I was playing through it one day....sounded fairly good...then the volume went down..then it came back..then it went down...adn did NOT come back up...it went silent. I shut it down. I wasn't haven't fun anymore. I feared that something that rarely happened had happened...but no, it was simply a case of an old, tired section in the multisection capacitor can giving it up. IT did not take anything else with it....like I said...usually such a failure doesn't harm more expensive and truly vintage-valuable transformers But, until I got the e-caps replaced and got the amp back on line, I didn't know that...I was anxious.
     
  5. Doctorx33

    Doctorx33 Tele-Afflicted

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    Death = Lack of fun. Permanent.

    Impatience = Burnt up PT and/or OT in vintage amp. Lack of fun. Permanent.

    Patience + caution + time + testing + modding amp to bring it up to spec = Fun. Permanent.


    I ****ing love logic.

    Also, Xtra points to Wally for quoting Robert Frost in this thread.
     
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  6. Ripdoozer

    Ripdoozer Tele-Meister

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    Thanks for your input, but this portion of your "logic" is based on opinion. Not all would agree that....

     
  7. Ripdoozer

    Ripdoozer Tele-Meister

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    Hey guys,
    A couple more questions on this old amp.
    First of all, FYI, I have used it for four or five 4-Hour gigs over the last year. I has worked well and sounds great.
    I am thinking that I will take it in and get it tuned up so I can use it on a more regular basis.
    I do want to try to throw an 8" driver in it, since there's room for one. Wanna see if it sounds a little more full. I am having trouble finding info about impedance. I know the amp if 5W.
    So, I was thinking a Jensen MOD (or something comparable) 8" - 20 Watt - 4 Ohms.
    Does that seem to be an adequate replacement?

    Thanks!
     
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  8. printer2

    printer2 Poster Extraordinaire

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    Disconnect a lead to the speaker and measure the voice coil resistance. This will tell you if you have a 4 or 8 ohm speaker.
     
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  9. Ripdoozer

    Ripdoozer Tele-Meister

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    K. I will double check. Everything I have found on line says its a 4 Ohm.
     
    Last edited: Feb 1, 2018
  10. Ripdoozer

    Ripdoozer Tele-Meister

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    What else would go along with replacing the speaker in this amp? I compared the images of the amp from Reverb that was posted in post #2 of this thread with my amp, and it looks like some things have been moved and some wires have been added. It looks like I cant just disconnect the old speaker and connect the new one. Is that correct?
     
  11. JuneauMike

    JuneauMike Friend of Leo's

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    I'm a recent convert to Alnico speakers, I love how they interact with the power that's being run through them. If your amp has an alnico speaker, I'd stick with that. Ceramic will respond differently, they'll have a different character. Not bad, just different.

    Also, modern speakers are so much more powerful and efficient I'd be mindful of that too. Part of the charm of the old amps is the underwhelming speaker performance. IMHO.

    Seems like your first priority is to address the shock hazard, the thing that threatens human life. And it sounds like you've got that taken care of.

    It may be difficult to think about changing electrolytics and other components in the amp, but as I understood your earlier posts someone else has already been in there jacking around with things. So any "true vintage" value that you might think exists is already a little compromised. Hopefully that eases your trepidation to swapping in more modern components.

    I never stumble across great finds like that. I'm jealous.
     
  12. Ripdoozer

    Ripdoozer Tele-Meister

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    Yeah. Good point.....I will probably just have the components updated and keep it as is for a while.

    As far as "Value"...it was my step mom's amp, and I think she would disown me if I ever sold it.......rightfully so.
     
  13. Ripdoozer

    Ripdoozer Tele-Meister

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    What is that extra rectangular piece that is on the speaker by where the leads connect? Does that component need to remain if the speaker is swapped out?
     
  14. JuneauMike

    JuneauMike Friend of Leo's

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    Ha, here's where the fun begins.

    Consult the schematic in Post #7. That rectangular piece has a purpose.

    https://robrobinette.com/Reading_Tube_Amp_Schematics.htm

    (But also, if you are taking it to a tech, he can answer that question for you.)
     
  15. Ripdoozer

    Ripdoozer Tele-Meister

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    Ok, could you please help me understand what that component is and whether it is part of the speaker assembly or part of the amplifier circuit. My best guess would be that it's the output transformer, and that it would need to be removed from the old speaker and mounted in the chassis, but I came here because i am not an expert and I am looking for assistance.

    Thank you.
     
  16. JuneauMike

    JuneauMike Friend of Leo's

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    Sure, and I'm sorry if I came across as a smarta**.

    It obviously looks like either a choke or a transformer. Based on the schematic and your pictures, my guess is that its the output transformer. I'm sure the really smart folks on this thread can fill you in on what it's doing there and what its job is.

    I'm enough of a newbie that I've never seen an OT mounted to the speaker. They usually are mounted to the chassis. But short answer, you need it, but you may not need it to be afixed there.

    I hope you take the time to read the link I sent and study your schematic. Its a cool feeling to know the entire signal path and the function of each components in your own amp. Not necessary, just a cool thing. And your amp looks simple enough that you could catch on quickly.
     
  17. Ripdoozer

    Ripdoozer Tele-Meister

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    It's cool man. I am sure "The Helpers" on this site grow tired of "The Helpee's" asking dumb questions.
    I am not trying to be annoying.
    Thank you for your help.
     
  18. JuneauMike

    JuneauMike Friend of Leo's

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    Here, just for funsies:

    The first schematic I sent is something I knicked from the web link I sent you. That's the signal path for the venerable Fender Champ, which Clapton supposedly used on Layla. Very famous tone in rock and roll.

    The second schematic is what folks believe is your point-to-point amp. (If you aren't familiar with "point to point" its worth your time to google the concept). I didn't think you could get a much more simple design than the Champ, but yours looks like maybe it is. Really cool.
     

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  19. printer2

    printer2 Poster Extraordinaire

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    I just skimmed the thread, thought you said you were going to get a different speaker for it, thought it might be good to get one with the right impedance for the amp. If you are not going to then it does not matter knowing how to disconect the transformer from the speaker, you heat up one of the puddles of solder where the wire goes into and lift it off. If you were going to do that you would have to do that anyway. The wire to the voice coil comes in from the other side and that is how the two wires are connected. If you were to swap out the speaker you would have to grind or drill out the rivet that is holding the transformer to the speaker. And it was common practice to mount the OT on the speaker way back when.
     
  20. Fiat_cc

    Fiat_cc Tele-Holic

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    I've not read the whole thread, so sorry if this is a dumb question, but could the square thing in the speaker make this a field coil speaker? My understanding is they have an electromagnet powered by a coil, rather than a regular permanent magnet. I'm not sure you can drop in s regular speaker without modification to the amp circuit if it is field coil driven.

    Edit: I just did some more reading, and it seems the field coil was also often used as a choke in the PSU, therefore if replacing the field coil speaker you would also need to find a suitable choke to add to the psu. I don't know if there would be other necessary changes.
     
    Last edited: Feb 1, 2018
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