My first Rocket... Need help!

[showsii]

Hello everyone,

This is my first post on TAG, and I'm excited to ask questions and get some great feed back from the very knowledgeable builders that I know frequent this site!

So lets get to it. I just finished my first rocket build. I ordered most of the parts from Rj, and sourced the rest from a local electronic shop here in Dallas. I followed the layout and schematic exactly as it is in the "rocket documents" file.

So in my amateur state of excitement I fired the amp up right after I had double and tripled checked joints and looked for any obvious mistakes. I did not however measure voltages before I fired her up. I am sure this is looked down upon, but I have never measured voltages before and actually need someone to point me to a good posting or website about how to safely and effectively measure voltages.

Pilot light turned on, no smoke and the tubes lit up. The tubes however did seem a bit bright compared to my spitfire. (the filament light that is).

Everything is functional, tone controls volume control ect.. (I also added the optional c4 cap on a mini toggle switch across R5, and a bright switch with switchable between 100pf and 500pf caps).

BUT! There is no head room! Is the amp suppose to be like this, the volume at 10 o clock is super dirty! It sounds great however, very smooth and rich. But I would assume I could get some cleans out of this amp? It is a tiny bit noisy with my guitar volume turned up, but with it turned down it is pretty quite, so I don't know if that is the amp or my single coils?

I know that I need to take some voltage readings to trouble shoot, So I would appreciate some help in that area for sure.

But any obvious ideas come to mind? This happen to y'all before?

I post pictures tomorrow sometime.


Thanks for the future help,

Ian

[overtone]

A warm welcome Ian!
I am little confused in trying to get an idea of your experience in amp building. Could you give us a more precise idea of that?
Are you saying that you are uneasy about how to measure the voltages?

You can compare your voltages to the ones published in the Rocket documents thread.

Best,
tony

[M Fowler]

I would use the voltage chart in TW files section measure the voltages and go from there.

I think Ron Worley's Express guide has info on voltage reading. TW file section.

Could be a bad tube as well if your positive the wiring is correct.

Mark

[showsii]

A warm welcome Ian!
I am little confused in trying to get an idea of your experience in amp building. Could you give us a more precise idea of that?
Are you saying that you are uneasy about how to measure the voltages?

You can compare your voltages to the ones published in the Rocket documents thread.

Best,
tony

Yes I would say I am uneasy about it. As far as my building experience goes, I have done 2 ceriatone kits before this. A spitfire and champ. This is my first from the ground up if you will. I am a beginner most definately.

I am going to go check the express build guide for the voltage reading information, and try to put voltages up today using the rocket voltage chart in the documents page.

Thanks guys!

Ian

[overtone]

I know how you feel, at first I never understood how you were supposed to take readings with one hand behind your back! Then I met an old radio ham expert and he gave me two Hirschmann probes, do you have something like these?

When you press the knob at the back a small clip comes out and you can connect your probes while the power is down. I use them about 90% of the time.
I am pretty sure that Farnell stock them. You may need the leads with banana jacks too.
This is called a Hirschmann "KLEPS30", maybe in the Sates you have other good alternative manufacturers.

[showsii]

I know how you feel, at first I never understood how you were supposed to take readings with one hand behind your back! Then I met an old radio ham expert and he gave me two Hirschmann probes, do you have something like these?

When you press the knob at the back a small clip comes out and you can connect your probes while the power is down. I use them about 90% of the time.
I am pretty sure that Farnell stock them. You may need the leads with banana jacks too.
This is called a Hirschmann "KLEPS30", maybe in the Sates you have other good alternative manufacturers.

Tony,

That's great, I went and bought some clips to attach to my multimeter, essentially the same thing as you posted? I did however get my nerves up and took the voltages. This was a big step for me ha.

Ok everyone, here are the voltages... Where do you measure the Secondaries, and how do I measure the mains?

Let me know what you guys think!

Ian

[overtone]

Briefly, across the board the voltages look close enough to me, except the heaters - tell us how have you measured your heaters? Where did you place your clips?
...got to take the dog out, hopefully some others will jump in too.

[showsii]

Briefly, across the board the voltages look close enough to me, except the heaters - tell us how have you measured your heaters? Where did you place your clips?
...got to take the dog out, hopefully some others will jump in too.

I will go back and re-measure the heaters tonight. I tried to get them as close to the pin as possible. Shouldn't they be around 3v though? (each)


Ian

[overtone]

Ian, I meant to ask where the meter probes were clipped to, sorry I was in a hurry, so:
if you have connected one clip-probe to the chassis / ground and the other clip-probe to one of the heater pins then the 3V is OK, - in tolerance.
But if you have measured across the two heater pins at the socket it is too low, by half.

[showsii]

Ian, I meant to ask where the meter probes were clipped to, sorry I was in a hurry, so:
if you have connected one clip-probe to the chassis / ground and the other clip-probe to one of the heater pins then the 3V is OK, - in tolerance.
But if you have measured across the two heater pins at the socket it is too low, by half.

Yes I measured from a ground on the chassis to each individual pin.

Maybe there isn't anything "wrong" but what if I ask the question... How can I get more head room out of this amp? What would be the steps to doing that?

Tony and Mark thanks for the help! Anyone else out there want to chime in?

Ian

[Ian444]

You could try disconnecting the C4 cap, just disconnect one end of it to try the idea, that should reduce the gain a little, might help or do the trick.

Is the volume pot a 500KA, as in *log* pot? Worth double checking just in case...

[overtone]

Is the volume pot a 500KA, as in *log* pot? Worth double checking just in case...

Yes, I was wondering about the taper on the pot too.

My last thoughts of the day:
- I would maybe be double checking my plate resistors on the preamp section then rolling some pre amp valves. I had a Telefunken from hell recently.
- Going by the voltage chart this is a 2 x EL84 Rocket, is that the case? I'm thinking the 2 x EL84 breaks up earlier than the standard Rocket.

Gone midnight here, ZZZ zzz

[showsii]

You could try disconnecting the C4 cap, just disconnect one end of it to try the idea, that should reduce the gain a little, might help or do the trick.

Is the volume pot a 500KA, as in *log* pot? Worth double checking just in case...

Ian,

I actually have the C4 cap on a toggle switch and can take it in and out of the circuit. The gain is significantly less out of the circuit how ever still kind of high.

I will double check the volume pot as well!

I have been reading some different posts about reducing gain and it seems maybe I can eliminate the C1 off of v1b's cathode to increase the plate voltage.

Does higher plate voltage on the preamp tubes mean more head room?

Tony,

It is a 4xEl84 rocket. I should probably measure those other two power tubes huh? HELLO.

Ian

[angelodp]

Here is a comparative voltage chart ( I do have reverb in the circuit ).

What speakers are you running and guitar.

[IMG2603]http://i260.photobucket.com/albums/ii9/ ... hart-1.jpg[/img]

[showsii]

Here is a comparative voltage chart ( I do have reverb in the circuit ).

What speakers are you running and guitar.

[IMG2603]http://i260.photobucket.com/albums/ii9/ ... hart-1.jpg[/img]

Our values look pretty similar, so that is comforting. I am running an American dlx Tele. SCN pickups. And I ran my Les paul, Tim shaw PAF pickups

Speakers- 1x12 cabs. One with a hellatone 30 (vintage 30) and the other Weber blue ceramic 50 watts. I did ran the cabs one at a time.

Update: I removed C1, the cathode bypass cap off of v1b. I think it helped a little bit. But still a bit dirty. Maybe try lowering the cathode resistor values off v1a or v1b?

Ian