"Test Rocket" - 10 lbs. of candy in a 5 lb. bag

[NickC]

Looks great!

Are those silicon rings on the rectifier tube?

Are the three holes above the impedance selector for bias test points?

[gktamps]

Thanks for that link. I was actually thinking of welding something up myself - have a very nice TIG welder. I have some perforated stainless steel, but was also thinking of a cage idea, with vertical round rods in front, sheet steel sides with handle slots, and a couple of horizontal rods at the top rear. I'd abandon that if something commercial would fit and look good though.

That's a great looking build! I've been thinking about the metal cage cab lately, too. Where ar you looking for manufacturers? I know Hammond makes them, and of course :http://www.lead.co.jp/rackcases/pdf/case/MK.pdf
But I havent sen any others. I think a birdcage would look cool, too...the Right birdcage [/quote]

[gktamps]

Hi NickC,
Yes, that rectifier came in a box of tubes I bought; someone applied silicone glue for some reason. The tube works well, and I just use it when testing new builds then stick it in a tray for next time.
Those three holes were indeed for test points, but the chassis was originally intended for a fixed-bias build of some sort. The previous owner had it drilled for the basic layout you see, with the can cap hole right above the preamp board, but I added holes for choke, 1st can cap, etc. I'll plug those when it's finished.
Cheers
GT

[overtone]

Ahoy Tony! How did you know I was a sailor? Lived aboard a Tayana 37 with my wife for 10 years.

Still have the strangled tone/low volume, but I suspected the high cathode voltage when I first took readings (you caught that, too), since it is so far over range, and haven't yet had time to correct that. I've got to get the voltages more in line, then evaluate again.

Screen resistor values are standard, but I had a brain glitch when I first wrote "cathode cap", meaning of course, "resistor". I changed that to 68 Ohms, which dropped the dissipation to where I can keep troubleshooting without toasting marshmallows.

Will make changes and report tonight.

Thanks, Tony,

Greg

Greg, good to see a tight space build. Tricky devils those.
Do you still have a strangled sound / low volume?

I had look at your voltages and the first thing that strikes me is the cathode voltage on V1a.

On the output section: what cathode and screen resistor values are you using right now? From here it looks like you have around 14W dissipation on each EL84 if it is a standard Rocket set-up. I don't follow the part in the OP where you said you changed out the cathode cap to get down to 9.5W.

Ahoy, tony

OK, with the 68R cathode resistor and 100R screens that looks all hunky dory.
I would check the cathode resistor of V1a, it seems to be a classic to grab the wrong value there.

Sailing and amp building keep your mind really sharp. Both the sea and electricity are totally unforgiving of mistakes.

I used to make the Golf de Lion rather unsafe in friends, 43 and 68 footers. Mostly I was suposed to be the navigator which was always interesting because anything magnetic goes absolutely berserk in my presence. Standing closer than six feet to the ship's compass would turn it into a whirling dervish. But I could consistently get us to a point exactly one mile from where ever we were supposed to end up.

[gktamps]

HAH!
Found the problem. Hooked up the cap and resistor (intended to decouple the grid to eliminate DC when using the VVR) to the wrong pin. Supposed to be grid, P2, and I've got it going to the cathode; 1M to ground will pump up the cathode voltage!
I might have to take a break from work to fix that and fire it up.
Thanks for tickling my brain, Tony.

[overtone]

good to hear!

Isn't that an Elan in your avatar?
I used to catch a lift to work with a guy who had a couple of those, this is going a while back. When we hit 100mph on the highway the cabrio roof would smack open.
In London he was racing all the bikers away from the lights and winning most of the time. Plus you had to kind of lie down in them.

[gktamps]

PM'd you, Tony,
GT

[gktamps]

Success. Had V1 wiring to pins 2 and 3 reversed. Dumb.

Sounds good, still running a bit hot on the power tubes, will take all new voltage measurements and make necessary adjustments. It's got one heck of a lot of drive, and I haven't even switched in the cathode bypass cap for V1's second triode. Pretty hairy.

One strange effect is the treble control does not work as standard - it gets more trebly from noon to full up, then just gets scooped from noon downward.

Another interesting thing is the boost pot; down below half and the treble gets rolled right off to mud. At noon, seems like it's at about neutral on gain and tone on the second triode, then gets nice and gritty from noon upward. With the pot turned down, it should just land C9 at ground, as well as the rest of the circuit to the other triode, making the effect transparent. Guess I'll have to decide how much that bothers me, and try to figure out how to correct it. Here's the circuit:
http://www.rjguitars.net/Rocket_Booster.html

Cheers,

GT

[gktamps]

Latest voltage chart. All standard resistor values except EL84 common cathode resistor, now 68 Ohms.