What am I missing with this amp ?

D'tar

Friend of Leo's
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Jan 11, 2013
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WNY
.I found a 0.001uf capacitor connected in series with the feedback resistor....there should not be a capacitor in the negative feedback circuit

How to "un-spay and/or un-neuter" your amp for Golden Tone!!!!

I found it had a 0.005 uF cap in the signal line. I looked at the schematic for your amp and saw the 0.001 uF going into the phase inverter

That 500pf >LTPI was pretty standard in fender head units paired with closed cabinets. Open back combos you will find the .001uf.... Look at the bandmaster head and any other AB763 circuits. That said I have heard of some gibby circuits that werer quite shrill for whatever reasons I have not investigated.
power supply caps being well over due for replacement
IMO... Always a great place to start.
 

Scooby9261

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Mar 10, 2017
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connecticut
Yeah i use to own a lot of vintage stuff, but once it got to be 45+ years old it was like a domino effect with parts failing and along with it tubes. One amp was a Twin Reverb i used for 20+ years. Was a 68 Blackface. I had no problems with that amp until a few years ago and first i had a preamp tube go on it at a show. I finished the show without fixing it, but i put a new tube in after the show. I warmed up the amp before the show and played thru it and it was fine. Half way thru the 2nd set that night another preamp tube goes. The amp still works so i keep playing it. Im suspicious tho because its the new pre amp tube i just put in. One more show and all the power tubes went and a fuse blew. Thats when i opened it up with a meter and started going thru the amp. (Now ya gotta remember im on tour in Wisconsin, i always have a meter with me and resistors but at the time i didnt have solder iron or anything to fix stuff with). I found that a few resistors were way out of spec. So i manage to find a soldering iron (I was at a Dennys at 4am discussing the amp with my roadie and someone in there was like "i got one you can use", total stranger mind you. So we follow the guy outside and sure as **** he has a nice soldering iron in his truck. He tells give it back when your done. I said im not sure how long it will take and he says kinda oddly "dont worry, ill be right here". Anywhoo so i fixed those resistors in the hotel room. Power it up and im good to go. I gave the guy back his soldering iron with $20 bill in the case. But Nope amp was not good to go, 1/3rd thru the next night (I remember this night because it happened at a weird point in a quiet part of Shakedown Street and my Mu-Tron made a sound ive NEVER heard in my life LOL) Amps all ****ed up again and now i have no tubes left. So i got stuck having to spend waaaaay too much money on ****ty tubes at a Guitar Center outside of Chicago. But when i went thru the amp again, more stuff had died. and this continued to happen the whole rest of the tour. Domino effect. Now i had a spare amp luckily, i tell everyone that if your gonna tour have a 2nd version of your tour rig. I know it costs money but i see musicians buy lots of equipment they dont need. You need a backup imho. And make sure your happy with your backup because you may need to play quite a few shows before you get your main rig back if at all that tour. Remember that.

But i did get the amp fixed up and never had problems with it again. That amp...

But i sold most of my older equipment off because the other ones had the same thing happen and at the time I had people who were willing to pay good money for it, they were gonna take it in either way. I didnt sell the amps without telling them this and that need to be replaced etc. But they were in working order at the moment. But once that domino effect happens, might as well replace just about everything in the amp other than some stuff ya know.

When this happened id been touring for years and i brought spare parts galore, but for some reason i didnt remember to put soldering iron into my stuff. But for how little it costs i always have caps, resistors, pots and input jacks in with my stuff that go to the amps i have on the road. I want to be ready for anything, because early on in my career i wasnt. After a rough tour in like 03 with gear i totally revamped what i was using and i made a list of everything in my amps, guitars etc all the little things and i bought what i needed. It also supplied my work shops drawers with resistors and caps and pots galore. I was seriously ready for anything either on the road or at home. But without that soldering iron !!! ya cant fix a damn thing. Your not always gonna be at a Dennys at 4am and have someone overhear your conversation and offer their soldering iron. Just saying :p lol
 

jeffhigh

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Dec 1, 2003
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190
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Australia
Maybe leave the capacitor in the NF Loop but bypass it with a resistor, or a pot to find that sweet spot where there is just enough bass response.
I had a playmaster 60w version (near identical circuit) back in the early 70's and also built one from a NOS Kit about 8 years ago, Nothing lacking in power,
 
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Burning Fingers

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Mar 6, 2019
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Australia
DOH...it is working fine now.

I recapped it but that didn't solve the issues of farting out and squealing on an 8 ohm load.

I realized that the too much bright in the amp was due to the NFB line being a Positive feedback line and the capacitor in the line was boosting the high frequencies.

The farting out, once I removed that capacitor , was due to all frequencies being passed back as positive feedback.

The anode cap leads were too short to swap them over as they were partially trapped under the OT...obviously someone had removed that transformer and put it back without a lot of care.

I freed the anode leads by loosening the nuts and bolts holding the OT in place and swapped the anode leads around.

Bingo... no farting out and no squealing on an 8 ohm load and a good balance of frequencies to go with the great reverb and powerful tremolo.

I felt stupid about not being able to figure out that the NFB was in fact Positive feedback sooner.


Thanks all for your input.

Now I am going to play through this sweet sounding amp for a while before the owner collects it from me.

😁
 

Burning Fingers

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Mar 6, 2019
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Australia
Maybe leave the capacitor in the NF Loop but bypass it with a resistor, or a pot to find that sweet spot where there is just enough bass response.
I had a playmaster 60w version (near identical circuit) back in the early 70's and also built one from a NOS Kit about 8 years ago, Nothing lacking in power,
I have a Playmaster 116 ( 40 watt ) and it sounds just as good as a Goldentone... a shed find some years ago
 




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