Hughes and Kettner Triamp mkII dead channel

[12AX7]

My Dad has a Hughes & Kettner Triamp mkII and channel 2A is dead. This is what I've checked so far, I unplugged the foot switch and tried switching channels from the amp, I tried replacing V1, V4, V5 with a 12AX7 I had on hand and I even tried swapping the original ECC83 in the V5 tube with the V4. There was no change. What should I check next? I have some limited knowledge of tube amps and have modded a Marshall JCM 2000 DSL 50 and a JCM 2000 TSL with the stable bias mod and a choke with the help from some of you guys. So I do know how to discharge caps and keep from frying myself. My schematic reading is limited I do know the basics but I do get lost on a large one and this amps schematic is huge and over my head (i do have a copy). I haven't taking the chasis out of the head yet and looked inside and was wondering if there are any test I should do on the tube sockets first? Are there any obvious failure points to look for inside? The first thing that came to my mind is that maybe a relay in the amp has gone bad? What would the relay look like and how can I test it? I have the tools to do the repairs including a capacitor tester that will test in circuit that I'm just dyeing to use for the first time. I have a pretty good stock of resistors on hand too. Any help would be greatly appriciated.

 

[KraftyBob]

That is quite the amp. 15 tubes - wow. If you’ve ruled a tube Id start by checking the relays that switch to channel two. Perhaps the signal is not even making that far due to a bad relay?

 

[Tatzmann]

Oh boy, dont really want to be that guy again,
but just get rid of it and buy something
simple.

At this moment there is only one problem,
who knows what the future brings failurewise.

What the future most definately brings is
much higher cost for tubes. Seeing this
thing and imagining the insides makes
me suspect that the investing in tubes will
not be equally paid back in tone.

Hope you can get it fixed somehow.

 

[12AX7]

That is quite the amp. 15 tubes - wow. If you’ve ruled a tube Id start by checking the relays that switch to channel two. Perhaps the signal is not even making that far due to a bad relay?

Questions:
1. Where would the relays be located?
2. What do they look like?
3 How can I test them to see if they are bad?

 

[12AX7]

Oh boy, dont really want to be that guy again,
but just get rid of it and buy something
simple.

At this moment there is only one problem,
who knows what the future brings failurewise.

What the future most definately brings is
much higher cost for tubes. Seeing this
thing and imagining the insides makes
me suspect that the investing in tubes will
not be equally paid back in tone.

Hope you can get it fixed somehow.

It's the old mans and It's a great sounding amp too. technically its' 3 channels but each channel has a second channel so it's really a 6 channel amp. It's a tone chasers dream but it does appear to be a beast to work on.

 

[KraftyBob]

The service manual for your dad's amp includes the board layout so that should help you identify the location of the components. Do you have a signal generator, dummy load and oscilloscope? If so, following the signal path on the schematic trace it out and see where it drops - that will help you narrow down the failed components. Honestly though, this is a pretty complex amp and you may be better off taking it in for service. It would be difficult at best troubleshooting this amp over a forum. Also, being that this is a Marshall forum chances are very few people have experience with this amp. Is there a H&K forum - you might get more responses there.

 

[12AX7]

The service manual for your dad's amp includes the board layout so that should help you identify the location of the components. Do you have a signal generator, dummy load and oscilloscope? If so, following the signal path on the schematic trace it out and see where it drops - that will help you narrow down the failed components. Honestly though, this is a pretty complex amp and you may be better off taking it in for service. It would be difficult at best troubleshooting this amp over a forum. Also, being that this is a Marshall forum chances are very few people have experience with this amp. Is there a H&K forum - you might get more responses there.

I do have a signal generator but don't have a scope. I do have all the parts to build a 4,8,16 ohm switchable dummy load including a BNC connector for the scope I just need to solder it all together. Terry from DLab on youtube gave out the parts list for the build and has a killer video on it. I did look briefly for an H&K tech forum but didn't see one.

 

[KraftyBob]

I do have a signal generator but don't have a scope. I do have all the parts to build a 4,8,16 ohm switchable dummy load including a BNC connector for the scope I just need to solder it all together. Terry from DLab on youtube gave out the parts list for the build and has a killer video on it. I did look briefly for an H&K tech forum but didn't see one.

You're 2/3 of the way there If you don't plan on getting a scope I guess you could always measure voltages with a DMM and see where they drop off, but for me it's much easier with a scope. Especially since you can see the quality of the signal as well as the amplitude. But there are techs that never use scopes so to each his own I guess. Not that I'm an "amp tech" though as I do this on the side as a hobby.

If you do plan on getting a scope an older dual trace 20MHz analog scope is perfect for amp work. And they're pretty cheap online these days. They typically handle higher voltages and are all you really need for amps. Keep your probes at 10x and always use AC Coupling (this blocks the higher DC voltages and protects the scope). There are other things you'll need to know about using a scope if you get into it. For signal tracing a 100mv, 1KHz sine wave is good unless the service manual specifies otherwise.

If you're checking resistor values make sure they are not in parallel with other resistors on the board. Capacitors should at least have one leg lifted from the board for a proper reading. Do a detailed visual inspection (with a magnifying glass if you have one) and look for burnt components, bad solder joints, etc. You mentioned channel 2A is dead, does 2B work? Also, does the light for 2A come on and there's no sound, or it doesn't even switch to it?

 

[12AX7]

You're 2/3 of the way there If you don't plan on getting a scope I guess you could always measure voltages with a DMM and see where they drop off, but for me it's much easier with a scope. Especially since you can see the quality of the signal as well as the amplitude. But there are techs that never use scopes so to each his own I guess. Not that I'm an "amp tech" though as I do this on the side as a hobby.

If you do plan on getting a scope an older dual trace 20MHz analog scope is perfect for amp work. And they're pretty cheap online these days. They typically handle higher voltages and are all you really need for amps. Keep your probes at 10x and always use AC Coupling (this blocks the higher DC voltages and protects the scope). There are other things you'll need to know about using a scope if you get into it. For signal tracing a 100mv, 1KHz sine wave is good unless the service manual specifies otherwise.

If you're checking resistor values make sure they are not in parallel with other resistors on the board. Capacitors should at least have one leg lifted from the board for a proper reading. Do a detailed visual inspection (with a magnifying glass if you have one) and look for burnt components, bad solder joints, etc. You mentioned channel 2A is dead, does 2B work? Also, does the light for 2A come on and there's no sound, or it doesn't even switch to it?

Great info! I do plan on buying a scope sometime soon after I do my taxes and pay Uncle Sam. I left the amp at Dad's until I get some idea of what to look for but if I remember correctly there's only a chA for each channel. For example, Ch.1 Ch1A, Ch2 Ch2A, Ch3 Ch3A no ChB at all but Ch 2 works Ch2A does not. The light for Ch 2 and Ch2A does light up on the footswitch and I'm almost positive it did on the head as well. I can go pick it up any time after work in the next day or two.

 

[PentodeLicious]

Take it to a certified H&K tech. that amp is a computer pretending to be a valve amplifier.
It will be really hard to get around and fix stuff in there(without breaking also other stuff on the way...)
It does sound amazing though.when it works...

 

[tully]

My Dad has a Hughes & Kettner Triamp mkII and channel 2A is dead. This is what I've checked so far, I unplugged the foot switch and tried switching channels from the amp, I tried replacing V1, V4, V5 with a 12AX7 I had on hand and I even tried swapping the original ECC83 in the V5 tube with the V4. There was no change. What should I check next? I have some limited knowledge of tube amps and have modded a Marshall JCM 2000 DSL 50 and a JCM 2000 TSL with the stable bias mod and a choke with the help from some of you guys. So I do know how to discharge caps and keep from frying myself. My schematic reading is limited I do know the basics but I do get lost on a large one and this amps schematic is huge and over my head (i do have a copy). I haven't taking the chasis out of the head yet and looked inside and was wondering if there are any test I should do on the tube sockets first? Are there any obvious failure points to look for inside? The first thing that came to my mind is that maybe a relay in the amp has gone bad? What would the relay look like and how can I test it? I have the tools to do the repairs including a capacitor tester that will test in circuit that I'm just dyeing to use for the first time. I have a pretty good stock of resistors on hand too. Any help would be greatly appriciated.

I have one
I love it
High gain, but not overly compressed
Channel 2B with a Maxon OD808 out front is stellar!
Channel 3A (or B) for solos
I like to set 1B for clean tones (don't use them much) because 1A doesn't get loud enough

 

[tully]

My Dad has a Hughes & Kettner Triamp mkII and channel 2A is dead. This is what I've checked so far, I unplugged the foot switch and tried switching channels from the amp, I tried replacing V1, V4, V5 with a 12AX7 I had on hand and I even tried swapping the original ECC83 in the V5 tube with the V4. There was no change. What should I check next? I have some limited knowledge of tube amps and have modded a Marshall JCM 2000 DSL 50 and a JCM 2000 TSL with the stable bias mod and a choke with the help from some of you guys. So I do know how to discharge caps and keep from frying myself. My schematic reading is limited I do know the basics but I do get lost on a large one and this amps schematic is huge and over my head (i do have a copy). I haven't taking the chasis out of the head yet and looked inside and was wondering if there are any test I should do on the tube sockets first? Are there any obvious failure points to look for inside? The first thing that came to my mind is that maybe a relay in the amp has gone bad? What would the relay look like and how can I test it? I have the tools to do the repairs including a capacitor tester that will test in circuit that I'm just dyeing to use for the first time. I have a pretty good stock of resistors on hand too. Any help would be greatly appriciated.

I would bring it to a tech