77 Boogie head (with fetron)

[kdove]

I have a 1977 boogie 100 watt head that is original. Still operating but while replacing the original pre-amp tubes to try to fix an occasional "breaking up" problem, I discovered the V1 "fetron". After doing some research, I think I found everything available on the fetron. Then talked to Mesa Boogie and got a bit of information from them on what needs to be done to replace with 12AX7. Although they have responded, they really haven't explained it really well yet ... exactly what needs to be done if I have to replace the fetron. I've got another information request for further clarification into them now.

My question: Anybody out there know exactly what needs to be done to replace fetron with 12AX7? Heard they had something on the Mesa website but it was nothing near a complete answer. In fact, I had the same paperwork in my files at home.

Also: What does it sound like if you make the adjustment? I've been pretty satisified with this amp for 30 years. However, since they stopped
using fetrons about a year after mine was made ... makes me wonder ... is it better without the fetron? Hard to imagine it being better?

Not sure that I'll ever have to change it ... it may not be the cause of my occasional problem ... but since they don't make fetrons anymore ... I'd like to know all I can about it.

 

[musicbox]

My understanding is that they used these solid state tube-replacement's to cure a problem with microphonics. Perhaps this was something to do with the early design of cascading gain stages and pre-amp gain. I would imagine that switching to a 12ax7 would warm up the tone, and add some compression and smoothness. Just the same as switching from a solid state amp to a tube amp, but perhaps not that extreme. Maybe you'd even find more gain. These are just assumptions and observations I've made based on logic and experience with guitar amps and boogies in general, as I have zero experience with the mark I.

If you love the way your Mark sounds, why change? Perhaps you can get your hands on a later Mark so you can compare the sounds, without having to drastically change the tone of yours?

You might also consider the consiquences of modifying an original boogie. They are exceedingly hard to find in original condition, so any changes made might detract from the value.

The best bet for fixing your problem would be to take it to an experienced authorized boogie tech, or just shipping it right to mesa/boogie for diagnosis and repair. You definilty have a little gem there and it would be a shame to have it raveged by some shmuck with a sauldering iron.

Sorry I can't be of more help, and that boogie was mostly useless. Good luck!

 

[kdove]

Don't get me wrong ... I haven't given up on Mesa Boogie yet. I still have an open request to them ... but it's NOT an old request. I do realize that they are all about making and selling new amps. But since I haven't had any trouble with this amp for 30 years, I have no experience with their service group ... it's a great product. But I'm throwing out feelers and trying to educate myself on this surprise fetron issue.

You're right about the experimenting on a classic amp. As you can imagine, I'm really concerned about adjusting it. What got me here is that I'm occasionally experiencing an intermitent decease in volume where the signal just seems to degrade and break up. I comes and goes occasionally. The fact is ... since the fetron is a solid state gizmo, it's probably NOT the fetron. I'm getting more pre-amp and power amp tubes to test the rest of the Boogie first.

I didn't know until last week there has been a solid state gizmo in my V1 slot for the last 30 years! BUT ... since they don't make these anymore ... I want to have a "plan in the bag" for changing it if it is the problem ... or fails in the future.

I have to admit I have at least a little curiosity about what it would sound like properly set-up for a 12AX7 (like 95% of all existing boogies). I mean ... could it be better? They must have had a reason for not using them anymore ... it's proably a half a dozen resisitors from being properly set up. And in all honesty ... selling it's not an option ... so the value issue is secondary ... but I'm aware I have something special.

 

[guitardaddy]

Isn't there a switch underneath on the chassis that you toggle for the Fetron or the 12AX7 ?

 

[kdove]

Isn't there a switch underneath on the chassis that you toggle for the Fetron or the 12AX7 ?

Not on my '78 ... later they did I think. But all fixed up with a 12AX7 instead and all the supporting cast of components. Working fine for quite a while now.