Calling all amp techs and schematic ninjas

[MississippiMetal]

I've having what seems to be tone-stack issues with my Hughes & Kettner Triamp on Amp 2. I have to dime the Master Volume on this channel to get any appreciable volume, and the treble control acts VERY strangely by increasing the volume slightly between 0 and 3, losing significant volume and signal between 5 and 7, and regaining some signal and volume while adding WAY too much treble between 7 and 10.

The bigger issue is that Amp 2 is, at it's absolute loudest, roughly 1/3 the volume of channels 1 and 3. This CAN'T be normal.


So in trying to figure out the interesting channel 2 issue on my Mk 1 Triamp, I discovered upon removing the chassis that a resistor spot next to the treble control was curiously blank, as if no resistor had ever been soldered in. This spot was designated R50. IF you'll take a look at the schematic below, it appears that R50 is a resistor to ground, connecting both the treble and the volume pots, of which seem to be the source of the problem.

Would an improper ground such as (possibly) this be a reason for the issue?

The schematic gives no denotation of value for such a resistor, so am I to assume it's a 1M-Ohm resistor to ground?

 

[wIsEbLooD]

you sure you do not have a bad preamp tube?
if there is nothing there in the amp and nothing there in the schematic then there is probably nothing supposed to be there.
on the other hand that schematic clearly shows a resistor there with no value.

 

[MississippiMetal]

I'm certain its not a bad preamp tube. This issue existed with both the stock preamp tubes and the vintage replacements I have in V4 and V5 now (which by the way worked in my 5150). The issue also existed with a pair of JJ ECC83s which are known good.

 

[wIsEbLooD]

look at resistor 49, it does not show a value either.
is that resistor in your amp?

 

[MississippiMetal]

I'd have to open her up again to be sure, but I'm fairly certain every resistor slot on that board was filled except for R50.

I'm thinking this was a factory durr-hurr, because the standby switch was installed backwards also. I flipped it around because it was bugging me. They must have had the new guy working when they built this one.

 

[wIsEbLooD]

that sucks man. they have a parts list in that pdf that includes everything but the resistors.

 

[MississippiMetal]

that sucks man. they have a parts list in that pdf that includes everything but the resistors.

I know!! I was bummed. It doesn't help that the resistors are all metal film, also.

I have had the absolute worst luck with gear lately.

My 6505+ has a squeal on the crunch channel that I spent 5 months trying to track down with no luck. I ordered a pair of Seymour Duncan pickups and the SH-4 was somehow weaker than it should have been, and now this amp I just bought has a problem.

And God forbid they be easy problems, like a bad preamp tube or even a bad capacitor, cold solder joint, etc. With everything I keep running into with my gear, I always get the head-scratch from amp techs.

 

[Anonymous]

Why don't you just call H & K support and put all speculation to an end?

Steve

 

[wIsEbLooD]

yeah.

 

[MississippiMetal]

Why don't you just call H & K support and put all speculation to an end?

Steve

I sent them three emails regarding this. Two of them were sent today. One was a "Okay, why haven't I gotten a reply?" and the other was sent from their website's form function, just in case sending a message directly from my email to theirs wasn't going through.

So until I get this sorted out, this is the 2nd Tube Turd I've got on my hands that I can't even sell, let alone use to its fullest extent.

 

[Anonymous]

Why don't you just call H & K support and put all speculation to an end?

Steve

I sent them three emails regarding this. Two of them were sent today. One was a "Okay, why haven't I gotten a reply?" and the other was sent from their website's form function, just in case sending a message directly from my email to theirs wasn't going through.

So until I get this sorted out, this is the 2nd Tube Turd I've got on my hands that I can't even sell, let alone use to its fullest extent.

I understand. Still... find a phone number and call them. That is what I'd do...

Steve

 

[MississippiMetal]

Why don't you just call H & K support and put all speculation to an end?

Steve

I sent them three emails regarding this. Two of them were sent today. One was a "Okay, why haven't I gotten a reply?" and the other was sent from their website's form function, just in case sending a message directly from my email to theirs wasn't going through.

So until I get this sorted out, this is the 2nd Tube Turd I've got on my hands that I can't even sell, let alone use to its fullest extent.

I understand. Still... find a phone number and call them. That is what I'd do...

Steve

Unfortunately there doesn't seem to be an available phone number listed for them.

 

[Neeklaus]

found this in the back of a H&K manual....

Hughes & Kettner
Wendelinuspark
Tritschlerstr. 3
66606 St. Wendel, Germany
Tel: +49 (0) 68 51 - 905 0
Fax: +49 (0) 68 51 - 905 103
International Inquiries:
Fax: +49 - 68 51 - 905 200
hkinternational@hughes-and-kettner.com

I would imagine you should need to use the international inquiries contacts...

dunno if this helps but thought it was worth posting!

 

[titanamps]

i'd suspect a bad treble pot, based on what you describe. the fact that there is no given value for R50 tells me it's not used. there's no reason that it not being there should cause the issue you describe, either.

to test the pot, check resistance between lugs 1 & 2 as you rotate the pot. it should change smoothly, not jump or read open. also, check resistance from lug 1 to lug 3...the resistive element may be damaged. sometimes brand new components are bad...

good luck.

 

[Gainiac]

Why don't you just call H & K support and put all speculation to an end?

Steve

I sent them three emails regarding this. Two of them were sent today. One was a "Okay, why haven't I gotten a reply?" and the other was sent from their website's form function, just in case sending a message directly from my email to theirs wasn't going through.

So until I get this sorted out, this is the 2nd Tube Turd I've got on my hands that I can't even sell, let alone use to its fullest extent.

not to get OT, but what was the story with the first one? you have problems w/ that too?

 

[MississippiMetal]

Why don't you just call H & K support and put all speculation to an end?

Steve

I sent them three emails regarding this. Two of them were sent today. One was a "Okay, why haven't I gotten a reply?" and the other was sent from their website's form function, just in case sending a message directly from my email to theirs wasn't going through.

So until I get this sorted out, this is the 2nd Tube Turd I've got on my hands that I can't even sell, let alone use to its fullest extent.

not to get OT, but what was the story with the first one? you have problems w/ that too?

 

[Giga]

If anything, physically adding R50 would even lower the total signal coming from the tonestack as it is a bleed to ground.

I'm with Titan amps on this; most likely a faulty treble pot.

Giga

 

[MississippiMetal]

I pulled the chassis and tested the treble pot, and it measured fine once I was able to keep the leads from touching the pot case or each other (tight fit). It ohm'd out at a max 233k and it receded back down to 0 as you would expect from a healthy pot. So i dunno what the hell is going on.

I just roll the treble all the way back to get the max volume and bass I can get, dime the master volume and put the gain up between 7 and 9 to get some high end back in there. It actually sounds really good for classic rock like 70's Rolling Stones and Bad Company.

 

[JerryP]

This is just on one channel? The first thing I'd be looking at is the LT3011 optocoupler.
Jerry

 

[MississippiMetal]

The optocoupler is supicious, but i have no reliable way of testing it, since I don't have an AMM. What's more, it looks like procuring a new one is going to be a pain in the ass.