Carr Sportsman - bought yesterday and it has a strange buzzy overtone

Sharky77

@GavRichList ;

Very interesting!

Which of these did you go for? I can't decide!

https://www.hotroxuk.com/tad-6v6gt-str-redbase-premium-matched.html?utm_source=GoogleBase&utm_medium=organic&gad_source=1

https://www.bax-shop.co.uk/amp-valves/tube-amp-doctor-6v6gtb-str-premium-selected-pair-of-power-amp-tubes?utm_source=google&utm_medium=organic&utm_campaign=surfaces&utm_source=google&utm_medium=cpc&utm_campaign=17858053119&utm_term=&adgroup=&creative=&gad_source=1

GavRichList

The first ones you linked, from hotrox 

Power_Freak

Before spending on new power tubes it's worth checking the preamps with some known quantities (I assume you have some lying around). It's unlikely but it could be a PI tube gone rogue - given you just got it shipped to you it could have got damaged en route. Won't cost you anything to rule it out (assuming you've got spares - if not you can re-order the existing ones to check if the noise reduces/increases)

Alex2678

I bought mine from here given hotrox reputation https://valvetubeguitaramps.com/product/6vtad-6v6gt-str-redbase-premium-matched/

Modulus_Amps

MikeP said:

Modulus_Amps said:

You say it doesn't do it with the headroom control up high or higher? So high headroom setting and on the edge of breakup.

The trail sound is horrible, it could be a faulty part or could be related to the headroom control implementation. The fact that Steve has said to use an OD pedal makes me think it is something inherent in the design

I suspect the headroom control is a voltage control for the power amp. It would also need to adjust the bias voltage for the power amp since it is fixed bias. When you change the voltages in the power amp it could affect the harmonics and overtones as the amp moves away from its intended operating point.

Err, that's what I just said, isn't it, err,  just with clarity and knowledge... and expertise...

Ha ha I missed your post on account it takes me hours or sometimes days to actually push the "post Comment" button

Power_freak is right in that it could be a badly unbalanced Phase invertor valve too. Easy to swap valves around to prove that.

ICBM

That sounds like either a bias problem or only half the power stage working - the output waveform is distorted, not in the usual 'musical' way. It could be from the phase inverter, although I would suspect one half not outputting a signal rather than simply being unbalanced. Check both the power valves and both halves of the PI valve are glowing correctly as a first check.

I'm not familiar with this amp or the implementation of the power scaling though. (I'm not a fan of power scaling.)

Sharky77

Solved!! 

Thank you much to everyone that chimed in.

I pulled the PI tube and the glass near the pins has a green mark on it. Didn't have any spare AY7s only AX7s so I pulled V2 and used that and now it works as it should! No weird buzzy overtones. 

Not sure what would have made the tube go like this - does anyone know if it's a sign of something inside not functioning properly which will just ruin every PI tube? 

Wazmeister

Just the tube mate - glad its all sorted 

Modulus_Amps

Good stuff, please let Steve Carr know. Might help someone else in the future.

Nothing in the valve will leak green like that, could be that someone used a marker on the valve when selling them so that dodgy returns could not be done easily. I would open the amp up and just check everything else around that socket. See if Steve used green goo in the amp etc

Make sure you have the right type of valves in the right places too.

ICBM

A 12AY7 as the phase inverter? That doesn't sound right. As I said I'm not familiar with this amp, but off the top of my head I can't think of any other amp which uses one for that, and I doubt it's a good choice. Normally it would be a 12AX7 or 12AT7.

A 12AY7 would normally only be used in V1, or occasionally in another position where it is effectively still the first valve, depending on the chassis layout. Is it possible someone has put the wrong valves in the wrong places?

Sharky77

Sorry it is an AT7, it's because it's a JJ it says ECC81 and I was just getting mixed up. Sorry for the confusion and thanks for the help! 

I will definitely let Steve know what the problem was and hopefully this thread will help somebody in the future

ICBM

Sharky77 said:

Sorry it is an AT7, it's because it's a JJ it says ECC81 and I was just getting mixed up.

In that case I think it's just faulty! It may look like it's working, but still not be working (or not properly) on one side - if so that would certainly give the kind of sound in the clips. I don't think the green mark has anything to do with it, and I doubt there's any fault with the amp which caused it - valves just fail sometimes.

Power_Freak

Power_Freak said:

 It's unlikely but it could be a PI tube gone rogue - given you just got it shipped to you it could have got damaged en route. 

I guess a broken clock IS correct twice a day after all?!? Not often I call these sorts of things!