hello all,
I just picked up a Trinity amps Tweed ( not a kit ) with power scaling ( VRM ). The bright channel is working good, but when I plug in the normal channel I get a farting/spitting sound on attack and eventually, the sound cuts off. I tried replacing tubes without any change. I quickly looked for a loose wire or component on that input but couldn't find anything. Could this be related to the power scaling module ? could a bad DC blocking cap do this ? Actually I could argue the bright channel is showing a very early breakup that seems a bit out of character... As you can tell, not a tech speaking here, I am a player, not a builder ! Please help me figure this out.
The interaction between the volumes doesn't seem to be what I am used to with 5E3's but if there is an issue with the input of the normal channel, that would likely have an impact I believe. It as been impossible to get anyone at Trinity, I actually have been trying to get in touch for weeks but not getting answers to emails or phone messages. If anyone knows something, please advise !
Any ideas/suggestions will be highly appreciated.
P.S. I have been incapable to reach Trinity for several weeks. Does anyone know somthing ? Still in business ???
Claude
Tweed deluxe spitting at me !
Moderators: pompeiisneaks, Colossal
Re: Tweed deluxe spitting at me !
Shouldn't have anything to do with power scaling. Assuming one channel is working mostly fine, your problem is between the input of the amp and the input of the second preamp tube. You are correct that intermittent stuff is often a loose connection, but this isn't always obvious from a visual inspection. Make sure the input jacks and the volume pots are tight. Try wiggling the first preamp tube to see if that makes it cut out. With the amp on, plug in an mp3 player or something to put noise through the amp. Your guitar strings are grounded, so it's better to avoid the temptation to touch them while messing with the inside of an amp. Using something non conductive, like a chopstick, poke everything connected to the volume and tone pots, the first preamp tube socket, and every solder joint on that half of the board. Do this with one hand on the stick and one hand in your pocket to avoid shocking yourself. With any luck, that will point you toward the problem, otherwise, you will probably need a multimeter to troubleshoot any further. I am not familiar with Trinity so can't give you specifics to that amp and I don't know how close they replicated an original 5e3 but poking stuff works for every amp...
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Stevem
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Re: Tweed deluxe spitting at me !
If the amp has a effects loop try jumping the send and receive jacks with a guitar cable.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Tweed deluxe spitting at me !
If you plug into the offending channel, hit a chord and it goes BLATT and fizzles out, then you wait a few seconds, try again, and it does the same thing, it's likely a filter cap.
Re: Tweed deluxe spitting at me !
Wouldn't a filter cap affect both channels ? DId you mean a coupling cap ?
Re: Tweed deluxe spitting at me !
Filter caps can do some interesting things depending on current demand. But that is neither here nor there. Have you carefully inspected the preamp tube socket to ensure that there is no incidental contact between pins? Wire ends gently brushing each other or a tiny drip of solder that slipped down between the pins? That's a simple variable to eliminate.
Re: Tweed deluxe spitting at me !
I did look very carefully for such unwanted contacts, found none. I am at a loss, eveything feels solid, all connections seem good, nothing I can "tap" give any indication. thre are two unusual things about this amp. The voltage regulation module "VRM" and there is a "pull" switch on the tone pot that seems to add ( or filter less ) mids... I.ll post pictures. The schematic and layiout available on the Trinity site does not show those, at least not completely...
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Re: Tweed deluxe spitting at me !
Do you have a multimeter to check B+ voltages? That could be very helpful. A bad plate resistor could kill one channel and make the other a little funky. If all the plate voltages are good then a coupling cap becomes a more likely suspect.
Re: Tweed deluxe spitting at me !
I do have a multimeter. Any chance you could use the schematic I uploaded topoint me to test points ?
Re: Tweed deluxe spitting at me !
V1 plates should be somewhere around 100-160v DC (pins 1 and 6)
Cathodes should have a wire across the tube socket connecting them so they should be the same voltage, probably around 2v DC (pins 3 and 8 )
Shouldn't have much, if any, voltage on the grids if no signal is present.
If the problem is only with one channel, It won't be a filter cap, but it could be a faulty coupling cap. There should be the same voltage as the plates on one side of the first two coupling caps, there shouldn't be any on the other side.
Another possibility is a broken, loose, or dirty tube socket. Wiggling the tube while you play the amp should make it act up if there is a loose or broken pin. Can also try to clean it, with the amp off, using electronics cleaner and/or rubbing alcohol and a toothpick. Make sure this is completely dry before reinstalling the tube and turning the amp on.
Cathodes should have a wire across the tube socket connecting them so they should be the same voltage, probably around 2v DC (pins 3 and 8 )
Shouldn't have much, if any, voltage on the grids if no signal is present.
If the problem is only with one channel, It won't be a filter cap, but it could be a faulty coupling cap. There should be the same voltage as the plates on one side of the first two coupling caps, there shouldn't be any on the other side.
Another possibility is a broken, loose, or dirty tube socket. Wiggling the tube while you play the amp should make it act up if there is a loose or broken pin. Can also try to clean it, with the amp off, using electronics cleaner and/or rubbing alcohol and a toothpick. Make sure this is completely dry before reinstalling the tube and turning the amp on.
Re: Tweed deluxe spitting at me !
Ok, on your posted layout, the two 100k resistors in a v below the two .1uf caps are your plate load resistors for v1 (your first preamp tube). The two .1uf caps are your coupling caps for those gain stages.
Measuring DC volts, place your ground lead to ground somewhere in the amp chassis. Then measure with the positive lead the point where the two resistors form a v (this will give you the entire B+ voltage feeding that node) then measure the opposite end of the resistors (this will give you the plate voltage of each half of your tube). The plate voltages should be noticeably lower than the node and very close to each other. It looks to be notated on the layout as 130v.
If one of your plates is way out of line, that's your problem. If it's all good, then on to the next component.
It might be interesting to test all of the notated points on the layout and see how your real world voltages match up.
Be careful poking around in there with the amp running, if you can alligator clip your ground lead that will give you one less thing to worry about accidentally making sparks with.
Measuring DC volts, place your ground lead to ground somewhere in the amp chassis. Then measure with the positive lead the point where the two resistors form a v (this will give you the entire B+ voltage feeding that node) then measure the opposite end of the resistors (this will give you the plate voltage of each half of your tube). The plate voltages should be noticeably lower than the node and very close to each other. It looks to be notated on the layout as 130v.
If one of your plates is way out of line, that's your problem. If it's all good, then on to the next component.
It might be interesting to test all of the notated points on the layout and see how your real world voltages match up.
Be careful poking around in there with the amp running, if you can alligator clip your ground lead that will give you one less thing to worry about accidentally making sparks with.
Re: Tweed deluxe spitting at me !
Well, All tension test points read within range. (at or very close to layout values)
I have to beleive this as to do with the VRM no ?
I do get 18V on the "other" side of the 3rd cap on the board ( 3rd orange cap ) wich sems to be correct since there is a link going under the board to the 1M resistor where that same 18V is specified.
I include some pics of the "pull" tone pot and the optionnal caps for the VRM on the inputs...
Claude
I have to beleive this as to do with the VRM no ?
I do get 18V on the "other" side of the 3rd cap on the board ( 3rd orange cap ) wich sems to be correct since there is a link going under the board to the 1M resistor where that same 18V is specified.
I include some pics of the "pull" tone pot and the optionnal caps for the VRM on the inputs...
Claude
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Last edited by hebaton on Fri Aug 11, 2023 11:05 am, edited 1 time in total.
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Stevem
- Posts: 4606
- Joined: Fri Jan 24, 2014 3:01 pm
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Re: Tweed deluxe spitting at me !
Since both sides (A and B) of your 12AY7 are idling , runnng off of the same cathode resistor and bypass cap that would leave these 3 possibilities for your issue in terms of the preamp section or the (12AX7 ) driver / pi section.
1) a bad 12AY7.
2) a bad .1 blocking cap on the brite output
A simple swap of these two .1 uf caps would prove that out.
3) a bad 100k plate load resistor.
Once again a swap would prove that out.
And yes you could read good voltage at the tube pin yet still have a issue when the tube is being driven with audio.
These are the easy things I would start with.
Ps.
I would start out by soldering a wire or placing a clip lead across the .1 uf caps off of the 68K resistors.
1) a bad 12AY7.
2) a bad .1 blocking cap on the brite output
A simple swap of these two .1 uf caps would prove that out.
3) a bad 100k plate load resistor.
Once again a swap would prove that out.
And yes you could read good voltage at the tube pin yet still have a issue when the tube is being driven with audio.
These are the easy things I would start with.
Ps.
I would start out by soldering a wire or placing a clip lead across the .1 uf caps off of the 68K resistors.
When I die, I want to go like my Grandfather did, peacefully in his sleep.
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Not screaming like the passengers in his car!
Cutting out a man's tongue does not mean he’s a liar, but it does show that you fear the truth he might speak about you!
Re: Tweed deluxe spitting at me !
Weird. I don't understand why they would have a power scaling thing coming off of the input... Yes, that could be part of your issue. Sorry, I was under the impression that any power scaling would be on the power supply or output like in every other amp I have seen and affect both channels. Totally agree with Steve, jumper that out and see what happens. Not sure if it is just the picture, but the solder on that tube socket looks really dull as well.