rocket head room

[brodie900]

Hi all,
im having some real issues with my rocket. It is essentially a ceriatone amp with heyboer trannies and better caps. All the values are the same as the layout on this site. When i first got it, it was quite clean and loud and i could turn it up to about 1 o'clock without much break up. I gigged it for a couple of weeks, ran my pedal board through it and it was fantastic but gradually the head room just seems to have run out! now i cant really use it anymore. its got loads of gain compared to when it was new and break up starts at about 9'30 on the volume. what the hell happened!? please help as i want my old clean rocket back!

[overtone]

two things:
did you try some other valves as a quick test?
did you check the voltages against the expected voltages for a Rocket?
best, tony

[brodie900]

yep done all the usual stuff like that and the voltages checked out fine. also since it happened nearly every component has been changed except for resistors

[overtone]

allow me to ask another couple of simpleton questions:
Do I understand correctly that the break up at 9.30 is without pedals?
Have you tried rolling back and riding the guitar volume?

We had a long thread recently that was about the Rocket headroom and after a full rebuild it actually turned out that a NOS tube for the PI fixed it.

My understanding is that the Rocket circuit will begin to break up between 10-12 o'clock, but is easily controllable through technique and/or guitar volume use. As I have only built two so far, perhaps others could expand on this.

[brodie900]

yep thats without pedals. its just not how it used to be, i could plug my tele straight in with the guitar volume up all the way and turn the amp volume to say 12 o'clock and it was still fairly clean. A little broken up maybe but it definately didn't have as much gain as it does now at the same settings. i noticed it happening slowly over about 4 or 5 gigs until my boost pedal for soloing didn't seem to work anymore because the amp was already so dirty that it wouldn't go any louder.

[lumox0013]

sounds like your amp is getting heavy use if you havent tryed swaping in different tubes I would go there next,also pull all the tubes drain the amp and check for resistor drift. I read in a thread that replaceing R4 with a 120k will increase headroom mine breaks up at around 12-1 but I'm running a liverpool output trany @ 5.2k I tryed a 4k when I built it, BIG difference.it might be your output trany was breaking in? keep us posted good luck

[M Fowler]

If it is not the preamp tubes, power tubes or rectifier then I would checkout the volume control on your Rocket.

Also check the heater wiring around those preamp tube sockets.

Speaker change also should be considered.

Mark

[brodie900]

thanks for your help everyone! now i have a few things to try. i was completely lost on this one before and i really appreciate your input. ill keep you posted

[redshark]

If your rocket is built with stock values you should find a way to check bias on your power tubes. The bias on the rocket with the R27 50ohms resistor is pretty hot. The best set of power tubes for the rocket should be a matched set that doesn't draw so much current. Probably your power tubes were a set that draws too much current and therefore their life is short so the lack of headroom means that the power tubes are suffering...If that is the problem change the value of the cathode resistor for something larger.

[Gaz]

I personally think the best thing to do is measure the clean output with a scope. If it puts out 30 clean watts (I think a Rocket is more like 25 actually), then it puts out 30 clean watts. No matter where it breaks up on the dial, at least you know you're getting max clean power and the power/output section is okay.

[Gargoyle]

I had a similar problem with mine, I have the Ceriatone with the Heyboers and upgraded caps.
Mine turned out to be a Bias issue. After the headroom dissappeared I had the Bias measured and it was at 54ma .
Had it fixed and the Head room came back

[brodie900]

cool, i had no idea that bias could cause this. i just happen to have some spare bits lying around that might fix that

[showsii]

I had this same problem,

Tony mentioned this up earlier on thread. I did a poor job the first time around and thought maybe it was my lack of clean wiring or technique that causes some of this hairiness. So I redid the whole thing and I believe it came out looking a lot better than the first job. However It was a bit dirty for my taste.

What I learned from all the greatly experienced builders on here is that the rocket is just dirty period. So I would almost say that the head room you had initially wasn't right. The break up should be right around 10ish.

I put a NOS 12ax7 in the PI and cleaned it up a little bit, but honestly my tastes just changed because I really can't live with out this "lack of head room" anymore! It is pretty rock and roll once you get use to it and you always have your volume knob to back things down a bit.

I would say check your OT wiring on your selector because I thought I was running the same impedance from my head to my cab but in reality It was mismatched when I turned my knob to what I thought was 8ohms for example. The mismatched impedance can cause more or ALOT less head room.

But hey, what do I know.

[Cliff Schecht]

I run a 5751 in V1 with my single coils to knock down the gain a bit. With humbuckers I might swap the whole preamp tube set out for 5751's.

[brodie900]

ok so far iv checked for resistor drift and found nothing, changed r4 to 120k but that didnt help either. Next thing to look into would be bias but i dont know how to check it on a curcuit with 84's.

I had a similar problem with mine, I have the Ceriatone with the Heyboers and upgraded caps.
Mine turned out to be a Bias issue. After the headroom dissappeared I had the Bias measured and it was at 54ma .
Had it fixed and the Head room came back

gargoyle do you know what was actually done to fix your problem?

if thats not whats happening to my rocket then i think showsii might be right in saying that these amps are just dirty