Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: munkeyboy on April 27, 2023, 04:13:28 pm
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Hi all, it has been a while, but I'm starting up some projects I've been putting of for years. The first is a silvertone 1482 build. The silvertone is one of my fav amps so I wanted to build one from scratch. I've used @sluckey's layout file I found some years ago, with some added mods like cathode bypass, tone bypass, bright switch and channel jumping. I'm having an issue I can't trace down with the trem and hope someone can put a fresh pair of eyes on it.
Here are the issues:
When trem is on, it is very weak. Attaching an alligator clip or probing pin 2/7 (or the ground around 8uf), it improves. It doesn't make sense. The alligator clip isn't attached to anything on the other side, just clipping it on improves the strength. Note that the 8uf is on the end of the preamp ground bus. I added another ground point at the 8uf and now it works. I don't understand if it was grounded, why another ground point closer fixes the strength. Is my ground bus wire too small of a gauge?
When trem is off, I get a lot of noise. Probing pins 1,5 and 6 fixes this. Again, just hanging an alligator clip off of where pin 1 attached to the board, fixes the noise. Or even hovering my hand around the chassis has an effect, tho not like the alligator clip
Outside of this, it sounds great so far (minus channel jumping not working as expected). I feel like I'm missing something. Any assistance is greatly appreciated! Attached some a real pic and my layout for context.
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Connect the 6AU6 pins 2 and 7 to the negative side of C13 (10µF) filter cap. This will probably fix your crazy grounding problems.
I have no idea about your channel jumping mod because I don't see any input jacks!
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I have no idea about your channel jumping mod because I don't see any input jacks!
Yeah, DIY layout doesn't export them for some reason. I fixed the channel jumping however. see attached screen shot.
Connect the 6AU6 pins 2 and 7 to the negative side of C13 (10µF) filter cap. This will probably fix your crazy grounding problems.
I tried clipping 2/7 pins to C13 neg ground, doesn't fix the second issue of when trem is switch off. As before, I still have to clip something to pin 1 to remove the "throbbing" noise.
Also while on, the noise will be present if turning up the strength pot to the extremes. And when off, the noise will be present if turning the strength to anything other than the extremes. Speed and tone to some degree also have effects at full extremes. Got to be some weird ground issue.
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I have no idea about your channel jumping mod because I don't see any input jacks!
Yeah, DIY layout doesn't export them for some reason. I fixed the channel jumping however. see attached screen shot.
To be clear, this channel jump only works if plugged in to either instrument jack. It won't work if plugged into Mic jack. Maybe there is a better way IDK yet.
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I gave it a pretty close look. I couldn't see anything on the board mis-wired but on the other hand, can't see connections to pots and tubes clearly. One thing I always do with a problem like this is do continuity checks between solder joints and components
I'm a pretty big 1482 fan myself. So I'm hoping you get it all lined out. I'm interested in hearing about the final test/review with everything working. I drew up a schematic for a slightly modified Bright/Stock Channeled 1482 a while back I call the "Stray Cat" I might build one of these days, schematic attached (no trem)
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Thanks for tip. I need to go back over everything for sure. I did go over the pots and missed one solder on the bright switch. That didn't really help that I can tell. Moving the ground as sluckey suggested actually made things worse. Not sure how.
One thing I noticed is pushing around the 6au6 wires changed the noise for slightly better or worse depending on position. I tried moving them above the board and the noise got even worse. There is some interference happening that I didn't think would matter since they don't carry signal. I think this may come from the routing and length of the wires due to position of the tube socket. It was supposed to be between preamp and output tubes, but I punched the octal hole instead the 7pin hole.. so I had to move it. For some reason attaching an alligator clip to pin one and letting the unattached end hang out the chassis fixes everything. I tried a clipping a soldering heat sink (something short that stays in the chassis) and it didn't help. I'd love to understand this phenomenon. Besides the heater wiring, should I twist any wires in the trem circuit?
one thing of note; I have really long leads from the PT, since this is a test chassis/build and wasn't committing to shortening the wires until I know where I want to place the PT/OT. They are at the end of the chassis out of the way.
second note; pulling the trem tube fixes any excess noise as well. Tube works (i pulled it from my working 1482).
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Update, I'm going to close this particular issue. I think the issue was in the location of the 6au6 tube which crossed wires with output OT/tube wiring. But it could have been due to bad output tube wiring/sockets. I created an adapter to move the 7pin socket to between output and preamp so the tube wiring was short as possible. I then replaced my octal sockets because they were old ones I reused. Then I rewired all the tube socket connections and cleaned up the PT wiring. The board itself was left as is.
Overall it sounds good now, but a few sound quality issues I still need to clear up.
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Good Going! Also thanks for letting me know that sluckey had already done a layout on the 1482.I had no idea. I found it and made a copy. Having it laid out for me already, I'm already feeling the temptation :help:
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What size chassis did you use? My best guess is 2"D x 8" W x 12" L, just by looking at that last gut shot.
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What size chassis did you use? My best guess is 2"D x 8" W x 12" L, just by looking at that last gut shot.
Sorry for the late reply. I used 2.75x6x12 and the final chassis is 3x6.5x12. I bent the first one myself, but has my final professionally bent. Here they are in the cabs.
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I have one more issue with both builds that I don't have with the original 1482. Up until about 5-6 on the volume, everything sounds good. But once breakup gets a little more, there is a fuzzy or fizzy distortion behind the sound. Dimed, it almost sounds like a fuzz pedal on power chords, but sounds horrible on solo notes. This is consistent on both builds. It isn't like the flubby sound you get with a 5e3. I put a grid stopper (470k) on V2 pin 7, it may have helped a little, but not much. I put a 12ay7 and a 5751 instead of 12ax7s. This worked, but barely any breakup unlike the 1482. I've heard bad things about Sprague caps and I'm using one (8uf) in the filter cap position. Could this be it or should I start looking else where? If its not component related, I'm guessing it has to do with layout or tube placements somehow.
@sluckey, I'm not sure if you has the same issue with your 1482 build, but I'd love to hear if this was the case.
edit: added most up to date layout
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@sluckey, I'm not sure if you has the same issue with your 1482 build, but I'd love to hear if this was the case.
I never built a 1482. My drawing was for a forum member. May have been Platefire.
I did own a brand new 1484 back in the '60s. Decent amp for $150. Very cheaply built, just like all Sears consumer electronics of the day. All my parents could afford and I was glad to have it.
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@sluckey, I'm not sure if you has the same issue with your 1482 build, but I'd love to hear if this was the case.
I never built a 1482. My drawing was for a forum member. May have been Platefire.
Gotcha.
I did own a brand new 1484 back in the '60s. Decent amp for $150. Very cheaply built, just like all Sears consumer electronics of the day. All my parents could afford and I was glad to have it.
I'm a fan of the cheepo amps sometimes. 1482 has been my favorite so far, but the Dan electro DM25 was fun too, just a terrible reverb tho.
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I put a grid stopper (470k) on V2 pin 7, it may have helped a little, but not much.
update: a 680k grid stopper seems be closer to getting rid of this blocking? distortion. I'm a little bummed I had to add a grid stopper, but I think I am close if not spot on to the original 1482. It may benefit me to put this grid stopper on a 1m pot instead.