Hybrid amp question...

[GregJr]

I have a Fender Performer 1000, 100 watts.
It is a hybrid amp with a clean SS channel and crunch(1x 12ax7) channel.
I use this amp ONLY for the cleans. I have a 5150 for dirt.
My problem is, the last 2 gigs, the amp kept cutting out. I read online it is because of the preamp tube, the inside of the amp gets REALLY hot and affects some components and the sound cuts out.
My question is : Can I remove the preamp tube without affecting the normal functionning the of the clean channel?

Thx.

 

[BrianS.]

Re: Hybrid amp question...

A rather quick scan of the (quite complex) schematic looks like all signals...clean or distorted...go through the tube. However, you're not going to hurt anything by removing the tube to see if the amp still works.

 

[GregJr]

Re: Hybrid amp question...

Thanks Brian. I"ll try it and see.
If that doesn't work, can i replace the tube with something having the same socket that won't heat up??

 

[jon the art guy]

Re: Hybrid amp question...

There are ss tubes, actually. They cost a lot though. I'd suggest replacing the tube and buying a cooling system.

 

[dystrust]

Re: Hybrid amp question...

Jet City Retro Valves are solid state tube replacements. I've heard they don't sound that great, but it likely won't affect the sound of your hybrid amp all that much. Their 12AX7 replacement goes for $29.95 which isn't a lot more than higher end 12AX7s.

 

[BrianS.]

Re: Hybrid amp question...

Your problem may not be from the tube. It seems that there are some other parts that are prone to running at high temps that could cause problems. Spending a lot of money on a tube substitute probably wouldn't be a wise use of your money.

Probably time to take it to a tech.

 

[dominus]

Re: Hybrid amp question...

Your problem may not be from the tube. It seems that there are some other parts that are prone to running at high temps that could cause problems. Spending a lot of money on a tube substitute probably wouldn't be a wise use of your money.

Probably time to take it to a tech.

But what if it's the tube that's generating the most heat?

 

[BrianS.]

Re: Hybrid amp question...

But what if it's the tube that's generating the most heat?

I don't know, what if its not? I guess the smart thing to do would be to open the amp up and do some troubleshooting.

A short internet search indicates that there are some "step down" resistors that help set certain voltages that run at very high heat. I've seen that in Fender tube amps that have solid state relays and switches. Those resistors can and do burn up traces and melt solder joints. The fix for that problem is to raise the resistors up off the board. That solution may work for the amp in question. Someone also mentions Zener diodes that run very hot. Also, the power transistors may not be coupled to the heat sink well enough, causing the thermal cutout to engage. These are just a few problems I've read about in about 10 minutes of reading...haven't read anything about the tube yet. Plus, the tube runs at a very low voltage...as far as tubes are concerned.

Or, just take the tube out and see if the amp still works...I didn't scrutinize the schematic, but I'm pretty sure you need the tube in there for it to pass signal.

 

[Demanic]

Re: Hybrid amp question...

How about just installing a fan like you would do in a computer tower?

 

[Edgecrusher]

Re: Hybrid amp question...

Most hybrid designs run the tubes at really low volts. I dont know about this amp for sure but many are ran at only like 30 volts and really dont generate the normal heat expected from a tube, I wouldnt be so quick to blame it.

 

[jon the art guy]

Re: Hybrid amp question...

"Starved plate". Its a neat technique, but it doesn't really get the tube to act like a tube. More like a low gain transistor.

Which is what it is in the first place, really. Electronics is pretty cool. I had to reverse-learn that on my own.

 

[dominus]

Re: Hybrid amp question...

Most hybrid designs run the tubes at really low volts. I dont know about this amp for sure but many are ran at only like 30 volts and really dont generate the normal heat expected from a tube, I wouldnt be so quick to blame it.

It might be that way in 9v pedals, but probably not amps. No real reason to design it that way.

 

[Edgecrusher]

Re: Hybrid amp question...

It might be that way in 9v pedals, but probably not amps. No real reason to design it that way.

It is that way in some amps I certainly didnt say all and there is a reason... You can get stupid amounts of tube life if you only run it at 18 volts

Keep in mind too that some amps the tubes have been put in the design just so they can say they are there and functionally add nothing that a transistor wouldnt its just marketing hype... What was that old ADA single rack space power amp that had 2 12ax7's in it and the adds talked about all of its tube warmth...

 

[BrianS.]

Re: Hybrid amp question...

^Yep.

http://support.fender.com/schematics/guitar_amplifiers/Roc_Pro_1000_schematic.pdf

No real reason to design it that way.

Take a look at the power supply. They use a very simple (cheap) power transformer with one primary winding and one center-tapped secondary winding to get 3 different DC voltage rails. See those 5w and 10w resistors? Those are the ones that step the voltage down from 40vdc to 16vdc, and they get HOT. Same with the zeners between the rails. If they were to run the tube at a "normal" voltage of 150-200vdc, they'd have to have separate windings on the secondary for the high and low voltages, plus the PT would more than likely need to be built physically larger as well, not to mention the larger filter caps that would be needed. Also notice there is no filament voltage winding on the primary of the PT.

So, yes, there are "real reasons" to build it that way. The main reason being cost.

*Edit

If you look at how they are deriving the filament voltage for the tube, you will see that there is potential for a lot of heat build up there, too. Looking at the layout, the step down resistors for the filament voltage are in the general area of the tube socket. This could lead to the illusion of the tube creating the heat, when in fact it is the 5w wire wound resistors.

 

[ehdwuld]

Re: Hybrid amp question...

Does your amp have an effects loop?
Have you used it recently

The effects loop jack in both my amps
My Carvin Belair tube amp and
My Laney GC80A SS amp
Cause the same cutting out problem

Easiest thing to do is jump the loop
With a short patch cable

Worst case replace the jack

Or do as the others say
Either or

*(Sent from my durned phone!)*

 

[GregJr]

Re: Hybrid amp question...

Thanks for the many replies guys.
I will definately bring the amp to a tech, with the schematics, and ask him to take a look.