Bugera Trirec infinum - need help with repair.

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chikov
Posts: 271
Joined: Tue Nov 09, 2010 8:19 pm
Location: Houston, TX

Bugera Trirec infinum - need help with repair.

Post by chikov »

I am not a professional amp repair tech, but I know a lot about tube amps and I built several of them. I’ve met a few musicians here in Houston and they once in a while ask me to help them to fix their amps. I ran into Bugera Trirec infinum 100watt 3 channel valve (!) amplifier. It only works thru 1st (clean) channel but the other 2 you could barely hear the signal. I searched for schematics and none are available ( was able to find something similar but just a somewhat predesassor of this one). After looking inside I almost gave up right away, but I like a challenge and I like to use projects like these to learn new things. Here is the problem. On the pin 8 of both 5U4 tubes I get 455VDC, on the plates of all four of 6L6 I have 454VDC. The weird stuff is going on with the plate voltage of preamp tubes. On the closest to the input jack (V 11) I get 258V on pin1 and 207v on 6. On V10 I get 379V on 1 and 270V on 6. On V9 I get 435V (!) on 1 and nothing on 6 (!). V8 has 298v on 1 and 435V on 6 and V7 has about 276 on both plates. This is super strange. Usually high plate voltage means that the tube is not conducting any currant, but V9 has zero voltage on 6 altogether... does anyone has any Idea what might be going on here?
I will try to attach the “similar” schematic...
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frankdrebin
Posts: 131
Joined: Wed May 14, 2014 11:40 am

Re: Bugera Trirec infinum - need help with repair.

Post by frankdrebin »

Check out all the resistors connected to anode and cathode of any preamp tube, plus the ones in between every node from the main supply.
Did you change tubes?

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frankdrebin
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Re: Bugera Trirec infinum - need help with repair.

Post by frankdrebin »

Looks like a jcm900 schematic,but your amp should be kind of a boogie recto...

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Rockwell666
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Re: Bugera Trirec infinum - need help with repair.

Post by Rockwell666 »

check voltages on all pins of V9. but as stated before V9 components need to be verified. careful those boards lift very easily.
Stevem
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Re: Bugera Trirec infinum - need help with repair.

Post by Stevem »

I would bet that it's a issue in whatever type of set up the amp uses to switch between channels.
Do all of your pins 3 and 8 on every preamp tube read atleast 1 volt across it?
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chikov
Posts: 271
Joined: Tue Nov 09, 2010 8:19 pm
Location: Houston, TX

Re: Bugera Trirec infinum - need help with repair.

Post by chikov »

Stevem wrote: Tue Jan 23, 2018 11:54 am I would bet that it's a issue in whatever type of set up the amp uses to switch between channels.
Do all of your pins 3 and 8 on every preamp tube read atleast 1 volt across it?
Hmmm, I went ahead and measured dc voltages between my Cathodes (pins 3 and 8) and got quite a different pattern. On V11 it is .44V, on V10 2.5V,on V9 5.6V, on V8 134V(!), V7 - 0V...
Im curious, the voltage between cathodes, what does it tell us?

BTW, I did found a suspicious high temp marks on the Voltage supply PSB. it looks like some kind SS triode, triac that got hot (it does have a large radiator with a cooling fan on the other side. Here is the photo:
I wonder if it has anything to do with the problem?
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chikov
Posts: 271
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Location: Houston, TX

Re: Bugera Trirec infinum - need help with repair.

Post by chikov »

frankdrebin wrote: Mon Jan 22, 2018 7:00 am Check out all the resistors connected to anode and cathode of any preamp tube, plus the ones in between every node from the main supply.
Did you change tubes?

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Yes, V11 and V10 were fried, so I replaced them
chikov
Posts: 271
Joined: Tue Nov 09, 2010 8:19 pm
Location: Houston, TX

Re: Bugera Trirec infinum - need help with repair.

Post by chikov »

Rockwell666 wrote: Mon Jan 22, 2018 2:44 pm check voltages on all pins of V9. but as stated before V9 components need to be verified. careful those boards lift very easily.
It is hard to do. their PSB is covered with the black paint and with no schematic I do not know what those parts do and what they are... I began to like PTP amps more and more :-)
frankdrebin
Posts: 131
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Re: Bugera Trirec infinum - need help with repair.

Post by frankdrebin »

I bet this is a total rip off of a rectum fryer, that's why they covered the board and don't release schematic.

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