List of tips on how to test which tube is broken (Herbert)

[shadow070]

Hi all,

Its been a year since i retubed, again i have a faulty tube. These past 12 months i only got a max. of 10 hours on the Herbert.

Leo has helped me out back then, there where tricks you could do to see which part of the preamp or power section where effected. Maybe we can get a full list, perhaps as a sticky tread? ( ex. plug your guitar in the return of the switchable effects loop)

So, Leo or anybody, can you help me out with a list of things to try?

Problem:
The amp is turned on, fully. Only the guitar is connected and ofcourse the speaker.
I get a thin tone/sound out of all channels

 

[shadow070]

After having PM'd Leo before i whent trough the messages.
Assuming it was the preamp section i plugged the guitar in the effects return of the amp, i had a full clean tone out of all 3 channels, meaning the fault lies in the preamp section. I messaged him again and he confirmed.
While looking at the tube layout (in the Manual) the V3 affects all 3 channels, i replaced this one and the amp works again!

 

[Ventura]

Hi all,

Its been a year since i retubed, again i have a faulty tube. These past 12 months i only got a max. of 10 hours on the Herbert.

Leo has helped me out back then, there where tricks you could do to see which part of the preamp or power section where effected. Maybe we can get a full list, perhaps as a sticky tread? ( ex. plug your guitar in the return of the switchable effects loop)

So, Leo or anybody, can you help me out with a list of things to try?

Problem:
The amp is turned on, fully. Only the guitar is connected and ofcourse the speaker.
I get a thin tone/sound out of all channels

That could be preamp tubes - when was the last time you changed those?? Easiest thing to do with that is grab a new 12AX7 (you likely have a couple kicking around) and from V1 to PI slot, replace current preamp tube with the new one - take off standby, try amp - keep working the single tube swap down the line. This may alleviate the tonal issues you're having.

If the volume (master) is moved and there is little to no "swell" in the sound you're getting, yes, it could very well be power-tube related, conversely, have you checked all your PT fuses?? If a fuse was blown, it would knock a pair of power-tubes out of the power section, more fuses more power-tubes; but the fuse would have been blown due to an arc or something similar in the power-tube/poweramp section - but always good to check.

If it's power-tubes, you can remove pairs of tubes working from the outside in - on low low low volumes - and test.
The Herbert is a 6 power-tube amp and the correlating tubes are paired as follows
A C E F D B
AB = Pair One (furthest outside tubes)
CD = Pair Two (middle inside tubes)
EF = Pair Three (centre two tubes)

Also make sure you've tried different cables - power, guitar, and cabinet.
Cheers
Unkle Mo

 

[Ventura]

Have you observed the amplifier whilst on in a dark setting? To check the glow of all 6 power tubes?? Sometimes early on within a failure the colours shown are a dead give away, but not always.

 

[shadow070]

HI, what is a dark setting? The issue is solved but more knowledge is always welcome.

 

[Ventura]

HI, what is a dark setting? The issue is solved but more knowledge is always welcome.

A dark room with little light if any at all - so you can really inspect the colours of the power-tubes

What was the problem/remedy?? Thanks.

 

[shadow070]

After having PM'd Leo before i whent trough the messages.
Assuming it was the preamp section i plugged the guitar in the effects return of the amp, i had a full clean tone out of all 3 channels, meaning the fault lies in the preamp section. I messaged him again and he confirmed.
While looking at the tube layout (in the Manual) the V3 affects all 3 channels, i replaced this one and the amp works again!

@Ventura ....this
The amp is working as usual again so no need to check the power section. Either way thanks for the tip!