Adding a PIgnose G40V standby switch

[scottme]

Hi all,

Is adding a PIgnose G40V standby switch as easy as putting the switch on either HV secondary tap?

While I'm at it, as I overheated the primary on the pwr tran, can anyone recommend good replacement power and output trannies for the G40V? Also related, does amyone know what the primary impedence is on the G40V output tranny?

G40V schem:

http://www.blueguitar.org/new/schem/...gnose_g40v.gif

[stokes]

I would put the switch between the rectifier and the first cap connection.You could also put it between the rectifier and ground in place of that straight ground connection from the rectifier.Putting a switch on one of the HV secondary wouldnt work,you would still get ac in the non-switched lead.

[schraedertr]

The circuit is based on the 50W Bassman, and any good Bassman output transformer will work.

The power supply is simplified with a full wave bridge rectifier for the 324VAC output and no separate bias supply. This means you either have to find such a beast (I just replaced one with a new power tranformer from Pignose, $60 with shipping), or add some real estate to do a center tapped full wave rectifier like the Bassman CG6B or later so you can use a 50W Bassman power tranformer.

Tom

[Rob Mercure]

Scott,

Why do you want a standby switch? We've approached this issue lots of times on this forum and it's predecessor and the consensus is that for consumer power level tubes cathode stripping during idle really isn't an issue so a standby switch isn't necessary. There are hundreds of sucessful designs - including almost all HiFi and PA amps - that don't incorporate a standy switch that have run thousands of hours no needing it. And many Gibson and other's used a standby scheme that shorted out the signal to the output tubes but still left them with B+ and subject to striping.

I describe a standby switch as a "stage musician's security blanket" - that is, you've played a set and you really don't quite want to shut down your amp, especially if you've only got one with you, so you "idle" it during the break knowing that it's still running and ready to play again. Or at least that's the way it feels to me when I'm performing. But my "acoustic" amp that I built doesn't have a standby switch and I just shut it off.

So installing one a a Pignose is really just a not needed mod - just turn off the amp when you're not using it (and you really don't know how many times I've forgotten and left my amp on standby for days at a time when I should have just shut the dang thing off when finished).

Rob

[Robert M. Martinelli]

We've approached this issue lots of times on this forum and it's predecessor and the consensus is that for consumer power level tubes cathode stripping during idle really isn't an issue so a standby switch isn't necessary. There are hundreds of sucessful designs - including almost all HiFi and PA amps - that don't incorporate a standy switch that have run thousands of hours no needing it.

Hi Rob,
cathode stripping during idle is not an issue indeed, but there is another issue that I have dealt with in the past, and that I would like to describe/discuss, it' s related to the current peak heaters withstand when powering on amps without a standby switch. On my Vox V15 I was able to see the heaters turn on with a visible white "flash" before going down to their normal reddish/orange when powering on, and I thought it was due to the cathodes' thermal inertia; I added a stand-by switch "on the fly" and the power-up flash on heaters disappeared, so I made it permanent; so, IMHO, it' s not helpful in protecting the cathodes, but the heaters....

I think a stand-by switch can lengthen the heaters' life considerably.

Your thoughts?

Best regards
Bob

[Rob Mercure]

Bob,

This topic has been explored before and it seems to be a characteristic of particular brand/make tubes and models of amps. I've never observed this in a MacIntosh power amp - for example - nor the Bogen mixer that I converted to my acoustic amp. But Vox - in particular - was noted for this as were Mullard and other Phillips designed valves. I'm glad it controlled it in your case but I'm not convinced that this is a universal "cure" nor that there is any problem. But I do, as I mentioned, like to know my amp is still operating when I go back on stage so I'm not going to disable the standby on my Vibrolux.

Rob

[hasserl]

Hi all,

Is adding a PIgnose G40V standby switch as easy as putting the switch on either HV secondary tap?

While I'm at it, as I overheated the primary on the pwr tran, can anyone recommend good replacement power and output trannies for the G40V? Also related, does amyone know what the primary impedence is on the G40V output tranny?

G40V schem:

http://www.blueguitar.org/new/schem/...gnose_g40v.gif

I had to replace the power trans in one of those amps, I was able to get the power trans right from Pignose at reasonable cost and they sent it out quickly. That would be my suggestion, get it from Pignose. Just google up the company website and get the contact info from there.

[Enzo]

Heaters flashing has zero to do with the standby switch. If you add one, the tubes will still flash when powered up. Does it matter if they flash at poper on or if they wait until later?

As scary as that might look, how many open heaters have you ever encountered in service to tube amps? Other things will cause a tube to be needing replacement long before the heaters give way. I run a commercial amp repair shop, and I can count on one hand the number of open heaters I have encountered in the last few years. I am not aware of any amp that has amassed a complaint list of burning out tube heaters.

It is a solution looking for a problem to cure.

[Robert M. Martinelli]

Enzo,
you' re right ( as usual ) when you say it' s rare to encounter burnt out heaters when repairing tube amps, OTH it' s true that heaters do wear out much like bulb lamps ( after all they' re tungsten filaments too ) and I think it' s not good to have them "flashing" when powering up....even if the heater does not give up at once.

I thought the "flashing" I witnessed on my V15 had to do with the cathodes' thermal inertia, so I thought delaying the +HT would have made a difference and, as a matter of fact, adding a st-by switch on my V15 actually cured the problem, I never investigated this deeper, but it could be interesting for me to leave the st-by closed and measure/record the heaters' voltage/current at startup just to understand the reason for this phenomenon; I always get my stomach aching each and every time I don' t manage to understand something ( this means my stomach aches most of the time ).

As Rob pointed out, this happens only on some amps, mainly Voxes, but on my 1964 AC30, which has no standby switch, heaters glow up evenly to their "normal" color when powering up, and I never had a tube failure ( so far ), only normal wear, so I agree that, as Enzo said, " it is a solution looking for a problem to cure" on most amps, OTH, in some particular cases ( like mine ), it could be useful.

Regards

Bob

[Enzo]

The flashing is the heater itself, not the cathode. Some tubes do that and some do not.

[Steve A.]

Scott,

Why do you want a standby switch? We've approached this issue lots of times on this forum and it's predecessor and the consensus is that for consumer power level tubes cathode stripping during idle really isn't an issue so a standby switch isn't necessary...

Rob:

Maybe it is not necessary from a technical point of view but I do think that most guitarists would want a standby switch on their tube driven stage amps. Tubes seem to sound better after they have heated up and putting the amp on standby should help keep them warm- right? And more important you might not want any sounds coming out of your amps during breaks, but don't really want to turn the amps off either.

Not a necessity but a nicety...

Steve Ahola

[Rob Mercure]

Steve,

Didn't I describe it as my own "stage safety blanket?" <grin> But I really don't think it's worth the trouble to add one to a Pignose and I don't know if Scottme performs but if not then I'd discourage it 'cuz it's when using the amp at home that I tend to forget the amp - someone calls, the dog whizzes on the mailman, the slugs scream for mercy as the toads charge 'em, normal household distractions - and wind up leaving it on standy for hours or even days.

Just depends on circumstances and the amount of return one gets for the efforts.

Rob

[Gtr_tech]

The *only* open heater I ever encountered (that I remember anyway) in my 20 yrs of working on music gear happened on a new tube out of the box....an EI big bottle 6CA7. Worked for about 5 seconds and opened up.

[Enzo]

I'm with you. Of the open heaters I have encountered, a couple of them were in octal tubes where the solder inside the pins had failed on the heater pin. So it wasn't really a damaged heater in the sense we mean here anyway. Very rare event.

[Robert M. Martinelli]

Enzo,
I was concerned about heaters' life not in terms of having them burn out ( as everyone already said it' s a very rare event ) but about heaters' decaying prematurely ( lower their emission with time ) thus affecting tubes' performance - so I' d like you to shed some light on this : are heaters expected to glow evenly all along their lives ? I didn't think so, I know tubes decay because cathode emission worsen with time, and I ( seemingly wrong ) thought heaters were expected to decay as well.

Sorry if I didn't manage to explain my concerns better in my previous posts.

Thanks

Best regards

Bob