Rocket Dog build log

[xtian]

Kick me, it works! I played a little, quietly. Sounds great. Hum is reasonably low (best in my history of half a dozen builds). No odd sounds, all good.

The voltages are remarkably close to the supplied voltage chart (see attachment).

I plugged values into the Weber bias calculator <http://www.webervst.com/tubes1/calcbias.htm> and it figures 11 watts per tube, which is 92% of max.

Wow, this sounds really hot. Did I do the math correctly?

[xtian]

Played for about 30 minutes with Tele and Paul. I pronounce this amp RFA (really freakin' awesome). The tone controls are very interactive, and provide a lot of versatility. Beautiful, blooming harmonics when slightly overdriven, and downright mean and crunchy when wound up. Couldn't get the Volume above halfway without rattling all the windows--and unnecessary to even try. Amp LOVES my OCD pedal.

The 22uF cat bypass on V1a doesn't add as much gain as expected, only about 2 or 3 dB. Maybe because it's on the second stage, and I am used to the bypass cap on the first stage.

Anyway, all good. Very good. Going to let my client have the amp for a week, then maybe we'll tweak or not. Will build Rocket Dog #2 after spring break; that's when the comparisons will get interesting.

Thanks for all your help, TAG. Wait…I built it so fast, no one had a chance to respond to my build thread! Well, this last question is still important: Are my EL84s biased too hot?

Cheers, everyone! Happy Spring Break.

[RJ Guitars]

Xtian,

That is way cool... very nice job! I applaud you for looking at things from the non-standard approach and getting the ultimate sound out of her. You made short work of that parts package, did you sleep last week?

Thanks for sharing - Impressive work!

rj

[RJ Guitars]

...I plugged values into the Weber bias calculator http://www.webervst.com/tubes1/calcbias.htm and it figures 11 watts per tube, which is 92% of max... Are my EL84s biased too hot?...

I am going to edit my input here - After I had time to think about it I am wondering about that 92% number... I want to understand that better. Based on all the other values you've measured, historical data on these amps, and the fact that you are not red plating I'm thinking your not running it too hot... having said all that I want to dig in and understand things a bit better on your calculations...

This comes up pretty often concerning the Rocket circuit... yes they are hot but I'll go out on a limb and say that they are not "too hot". I did a ton of reading on the Rocket amps (and AC30) a few years back and I recall reading something on how you can get by with running tubes biased extra hot in a cathode biased mode where they would red-plate at the same bias level in a fixed bias amp. I am sorta thinking it was a Gerald Weber tech note but if I recall he was repeating something that Ken Fischer had said... anyway if we could get one of the electro engineering types like Cliff Schect or Andy Leblanc to comment on why that is maybe it would make sense.

When you run them hot no doubt you are shortening the life expectancy of the tubes but I think that means in number of years rather than months or hours in this case... or I could be entirely wrong and we still need one of the wizards to help us out here. Historically the AC30 has run that same cathode resistor value and it is key to the tone. You might look at the Dr. Z voltage specifications on his Z-Wreck and see how hot he runs the bias on his. He uses the Russian output tubes like you have and I'm sure he did his homework to dial those in for tone with a reasonable safety margin at the same time.

rj

[M Fowler]

Nice build.

Ever work on any Traynor amps? I was really surprised at the high voltage he designed those amps to run at. Probably why I had to replace the power tube sockets.

I used 300-0-300 for about three Rocket type amps and they are still purring nicely. Now days I reduced my amps to 280-0-280 and generally lower my dropping string voltages for a cleaner and quiet amp. But those tubes running hot really can deliver some sweet tones.

Mark

[Reeltarded]

lol wow like I missed a month of posting or something. Amp in a day. That's close to The Fowler Improbability of passing yourself in the hallway carrying the amp you were on the way to order parts for!

Not just fast work, very nice too!

[M Fowler]

Yeah he better slow down or they'll be hauling him to the hospital like they did me Just kidding

Very nice and fast work, I'm jealous.

[xtian]

That's close to The Fowler Improbability of passing yourself in the hallway carrying the amp you were on the way to order parts

So funny! Thanks guys. It was a novelty to build with these quality parts. It was like 'mas when the parts arrived. 16 hours over two days. I think the next one will take only 12 because I won't have to sit there so long wondering where to route some of the wires!

[sdp1234]

Nice build.

Ever work on any Traynor amps? I was really surprised at the high voltage he designed those amps to run at. Probably why I had to replace the power tube sockets.

I used 300-0-300 for about three Rocket type amps and they are still purring nicely. Now days I reduced my amps to 280-0-280 and generally lower my dropping string voltages for a cleaner and quiet amp. But those tubes running hot really can deliver some sweet tones.

Mark

I understand that it is difficult to generalize but would you say that in the Rocket Circuit (AC30) that lower Power Amp B+ would be cleaner than a higher B+?

Mine is running high at about 330 but i'm wondering how different it would sound if i changed the PT and ran at ~ 280-290?

[Zippy]

I understand that it is difficult to generalize but would you say that in the Rocket Circuit (AC30) that lower Power Amp B+ would be cleaner than a higher B+?

Mine is running high at about 330 but i'm wondering how different it would sound if i changed the PT and ran at ~ 280-290?

Have you adjusted the dropping string to restore the values of the preamp and PI voltages?

[M Fowler]

Like zippy said I would start with increasing the resistor size in the dropping string lowering the preamp tube voltages.

[xtian]

RJ's happy happy parts box arrived today, so I'm starting Rocket Dog #2. This one will get a VVR and a few lead dress improvements, but otherwise will be identical to #1.

I did the headphone trick again before mounting the trannies. Notably different than last time: the PT and OT were happy to sit in the predrilled holes this time, with just a little twist and push to get them to the lowest hum spot. The choke, however, was way different. I couldn't get it to hum at all, except by putting it right on top of the PT! So it's perfectly happy to sit where intended.

[RJ Guitars]

RJ's happy happy parts box arrived today, so I'm starting Rocket Dog #2. This one will get a VVR and a few lead dress improvements, but otherwise will be identical to #1.

I did the headphone trick again before mounting the trannies. Notably different than last time: the PT and OT were happy to sit in the predrilled holes this time, with just a little twist and push to get them to the lowest hum spot. The choke, however, was way different. I couldn't get it to hum at all, except by putting it right on top of the PT! So it's perfectly happy to sit where intended.

This is the experiment that I thought should have been done... or maybe has been done since so many of these amps have been built but the data has not been looked at very much. One guy can put his Wreck together by the book and have hum while the next guy has to get clever... I guess that is telling us that the field patterns and resulting coupling varies in each set of transformers.

This looks like you are off to a nice start on another build. You should be able to put one of these together in your sleep after this. I am hoping you'll get us some great sonic clips from your studio once you have this dialed to suit you.

thanks,

rj

[xtian]

I installed a Hall VVR3 on the front panel of RJ's TW chassis. It took a lot of visualizing and rotation of parts, but I think I arrived at the only valid solution. The Rectifier is mounted on the chassis with thermal paste and the mica sheet it came with, and the leads are extended to reach the PCB.

Can't wait to test it out!

[lions den]

Nice looking build. See you went with the filter caps re-alligned on this one as well. Assuming that's working out well, looks great.

sean