Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: plexi50 on September 02, 2022, 04:17:40 pm
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I am having an issue not being able to get the tremelo intensity pot to engage earlier on the dial. The trem wont come on until i am at 6 on the pot CWR. I an using the 6C4 schematic, :EDIT: 6G4 schematic as that is the closest one i can find for this amp. Is there a resistor that i can increase or decrease to obtain this?
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Never heard of a 6C4.
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I am sorry i meant to say 6G4 schematic. It a super amp with no schematic available. A thread online say the 6G4 is the closest available schematic. I have changed all the astrons out to Mallory M150 cap's. All electrolytic's have been changed. Phone cameras is messing up. Can't take other pic's at the moment.
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The 6G4 schematic follows my amp's tremelo section spot on. The 6G4-A is not even close.
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I can barely make out the numbers on the tube chart but i think I see 5G4.
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I presume you tried a tube-swap already? That’s the first thing you need to do.
If that don’t fix it, look for values drifting in old Carbon comp resistors in the trem intensity part of the circuit.
Then if that don’t fix it, look at replacing caps and/or resistors in the C/R filter network between the oscillator tube’s plate and grid.
But don’t just grab a soldering iron and start replacing parts holus bolus.
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I presume you tried a tube-swap already? That’s the first thing you need to do.
If that don’t fix it, look for values drifting in old Carbon comp resistors in the trem intensity part of the circuit.
Then if that don’t fix it, look at replacing caps and/or resistors in the C/R filter network between the oscillator tube’s plate and grid.
But don’t just grab a soldering iron and start replacing parts holus bolus.
Actually i changed the Astrons to Sozo cap's & i replaced all the resistors and cathode bypass cap's in the trem circuit already. The intensity pot reads 10 Meg.
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I found the problem. Some one in the amps history grounded the right lug of the intensity pot to ground and installed a .047 cap to the wiper of the pot. I lifted the far right lug from the back of the pot and put the .047 there. Works great! Just followed the 6G4 schematic.
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It was right before you messed with it.
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It was right before you messed with it.
It's a weird amp. Ok i see now how it goes. Either way the 0.47 winds up connected to the wiper. EDIT: No it wasn't working right when i got it. I always just replace all the old trem cap's and resistors.
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It was right before you messed with it.
It's a weird amp. Ok i see now how it goes. Either way the 0.47 winds up connected to the wiper. EDIT: No it wasn't working right when i got it. I always just replace all the old trem cap's and resistors.
I understand it was not working properly when you got it. But messing with the INT pot and that cap was not the right answer. The problem lies elsewhere. I hope you have reconnected the INT pot lug to ground and put the cap back on the pot wiper.
The circuit is not weird but it's not just a simple tremolo circuit as found in most amps. This short lived circuit is called a "harmonic vibrato" circuit and is more complicated than most common tremolo circuits. And the Fender schematic is not easy to follow. Look at my Revibe schematic (http://sluckeyamps.com/revibe/revibe.pdf) to see the same circuit but drawn in an easy to follow style. And look at page 14 of my Amp Scrapbook (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf) for a description of the 6G4 circuit if you care to understand what's going on.
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It was right before you messed with it.
It's a weird amp. Ok i see now how it goes. Either way the 0.47 winds up connected to the wiper. EDIT: No it wasn't working right when i got it. I always just replace all the old trem cap's and resistors.
I understand it was not working properly when you got it. But messing with the INT pot and that cap was not the right answer. The problem lies elsewhere. I hope you have reconnected the INT pot lug to ground and put the cap back on the pot wiper.
The circuit is not weird but it's not just a simple tremolo circuit as found in most amps. This short lived circuit is called a "harmonic vibrato" circuit and is more complicated than most common tremolo circuits. And the Fender schematic is not easy to follow. Look at my Revibe schematic (http://sluckeyamps.com/revibe/revibe.pdf) to see the same circuit but drawn in an easy to follow style. And look at page 14 of my Amp Scrapbook (http://sluckeyamps.com/misc/Amp_Scrapbook.pdf) for a description of the 6G4 circuit if you care to understand what's going on.
Yes i have the 0.47 cap back on the wiper of the intensity pot. I saw my error. Documentation is what this is all about for me. I will look at all your info. I have a strong 7025 in the third preamp socket. Thanks.
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PDF files wont open. Get Error Message: It's not my day! :l2:
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That's too bad.
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try to download it again. I've got it on my phone, on the netbook in the shop, and on my main laptop
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V3 and V4 are both in the tremolo circuit. Either could cause problems. Measure voltages on both tubes and compare to Fender schematic voltages.
So, you have no trem until 6 on the pot. Is the trem strong with the pot on 10?
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V3 and V4 are both in the tremolo circuit. Either could cause problems. Measure voltages on both tubes and compare to Fender schematic voltages.
So, you have no trem until 6 on the pot. Is the trem strong with the pot on 10?
Yes trem is very strong on 10. Only comes on at 5-6 on the dial. The speed pot is fine and goed from S L O W to blazing fast. All my other PDF files open. Checkin it out now on phone. Ok hold on i had to copy and paste the link in google and they both went straight to my download folder. They both open now. Yeah i have a computer problem for the last week i have to sort out.
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Yes trem is very strong on 10. Only comes on at 5-6 on the dial.
I'm not so sure this is an issue. :dontknow:
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Yes trem is very strong on 10. Only comes on at 5-6 on the dial.
I'm not so sure this is an issue. :dontknow:
I know what you mean. It's functional enough at 6 and on through 10. Some of these old fenders have this issue and some don't. That's what im trying to figure out. It really looks straight forward enough on the schematic. Your schematics are really nice. It's just bugging the h**l out of me because all the old Astrons and resistors have been changed. My eye was playing with my head earlier with that 0.47 cap on the intensity wiper. I was looking down at the ground. At this point i need to take a break for tonight. I know this circuit and have continuity tested every cap and resistor connection point/s. It works and sounds good. Just not until 5-6 on the intensity pot. I will find this demon! It will probably turn out to be something real simple and right in my face. But at this moment i'm baffled. It will all work out. Just can't wait to find the issue. The 10Meg pot reads and ramps up good on ohms testing. No dead or scattered jumps in ohms throughout pot. Yes going to measure voltage now.
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I have changed out (2) more Astrons on V2 and have the trem working at 3 now on intensity pot. I'm waiting on a few 0.01 cap's to arrive. I have all the voltages written down and they are all within a few volts of the schematic. Like 1-2 volts. Not a worry. Here are some decent pic's now. There are a lot of resistors on the schematic which are either not present at all or different from the amp as it came to me stock and untouched. Last Call Tonight.
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I had spotted a resistor discrepancy in the first pic you posted, but held my tongue because it looked like factory work. Look at this annotated pic and compare to the Fender schematic/layout...
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Steve
Your native name will be
Lynx Eye
😁👍👍👍
Franco
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Does an old lynx have cataracts? :icon_biggrin:
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:laugh:
I saw a wild hybrid Lynx in FL, I was close, but NOT that close, had NO desire to be that close
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Cant bee too bad for that lynx if he still can read resistors.
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I had spotted a resistor discrepancy in the first pic you posted, but held my tongue because it looked like factory work. Look at this annotated pic and compare to the Fender schematic/layout...
Yes i almost changed it to a wire but there is also a 56K resistor the 10K comes off from. 4.7M - 470K 326 VDC 56k 270VDC 10k 160VDC on pin 6. Should i throw in a 100K and remove 10K and put wire to pin 6? That's what the schematic say's. It was factory and i couldn't see why they built it that way. Maybe the fender guy had cats?
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I would make it look like the schematic/layout.
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I would make it look like the schematic/layout.
I will do that. Maybe they were experimenting back then. Who knows. Definitely has been a stress going back and forth over the published 6G4 schematic and invisible 5G4 schematic. Plus they also put the wrong tube charts on some amps back then. I'll Be Back!
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There are brand that are famous for schematic mistakes (may be they do It to ..... cover secrets ??)
Franco
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Changed 470K & 56K junction. Changed 56K to 100K and removed 10K plate resistor. Wire in place. Plate voltage went from 160vdc up 35 volts to 195vdc. Intensity pot has lost it's flavor at 3-4. Now clearly present on 5 again. Is there a cliff any where here in Floridah? :l2: I am going to use Allen Bradley carbon comps when this is figured out. EDIT: Nevermind that idea. I don't want to go through a bunch of NOS carbon resistors and chop them up. And yes i also know that could put me right back where i'm at now. Hopefully not.
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Look at all of these power supply cap's!
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Not aware of any cliffs in your area but there is a tall bridge and plenty of sink holes. :icon_biggrin:
Looks like the filter caps have been replaced.
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Not aware of any cliffs in your area but there is a tall bridge and plenty of sink holes. :icon_biggrin:
Looks like the filter caps have been replaced.
Yeah i replaced the filter caps last month. Odd 56K resistor values. Seen it once or twice before. There is the Sunshine Sky way Bridge here. But there are already plenty of Ghost's that hang out there. I need a trip to Cancun. Back in 1996 a ticket to fly was only $95.00 round trip. But that wont fix this amp. It sounded best and could be heard at 3-4 with the previous arrangement 56K & 10K plate. Speaking of Ghosts, i have one here. Isn't it crazy how (1) amp can give you so much trouble? If it came in hacked i could understand it. But it was stock all the way to my eye'z.
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Is there a cliff any where here in Floridah?
find the tallest waterfall in FL, it's in the pan-handle, If you sneak passed the tourist walk, and look down, it might pass as a cliff :laugh:
It's also a famous place, some not-so-smart person with too much money thought there might be oil in them there hills :think1:
aside:
I got the park Ranger in trouble, he let me run my metal detector around but I couldn't DIG!, I found a riggers camp previously not noted in the old survey. He was then obligated to report it, do all the paperwork......after that, every time I seen him he'd say "I DON"T WANT TO KNOW" :icon_biggrin: