EL84 rectifier amp

[tubedogsmith]

This is a pretty cool sounding amp. None of the highend hash you often get with EL84's.

[Mark]

Dear Tube Dog Smith

That is a cool looking amp. Do you get any slight noise from the tone controls (input to the P.I. stage)?

I really like the sound of these amps, but that noise did bug me. I will have to look into it in the future.

[Mark]

Dear Tube Dog Smith

I do realise after having a good look at your diagram that I do have a question. Why did you include the series resistor in the P.I. circuit?

In my efforts I did away with this resistor. What benefits do you this you get from it's inclusion?

As far as general questions about the amp go:

SoZo caps or Mallory 150's?

What transformer set?

power supply (resistor) values?

How is the 5AR4 holding up?

Again nice work.

[tubedogsmith]

Mark, this amp is dead quiet. Mallory signal caps. Any stiff PT that will give you around 300vdc on the output plates with a GZ34 will work. The OT has a 4k primary and is NOS. The series resistor into the PI seems to "thin" up the tone just a bit and tighten things up. Not real discernable at all but just enough. Power supply has one 18k and two 9k resistors. Have had a Sovtek GZ34 running in a circuit like this for over 3 years. I don't use the standby as such, I turn both switches on at once.

[PeteRH]

Great job on the Rocket clone. Have you been able to compare it sound wise to an AC30 to see how much difference there is?

Where did you get that chassis from? It compliments the build quality and setout. I built an aluminium chassis myself and it will be the last one. It is just not worth the effort. Mind you, it was much easier than the stainless chassis I built for my JTM45!! That was a real lesson.

I have just finished wiring a Liverpool style amp with a rectifier thrown in
for good measure. Actually i had to go back and clean up some wiring after seeing yours. I hope to fire it up in the next day or two and will post some pics.

Thanks for the photo. It helped with my build.....and maybe the rocket if I ever build it.

Cheers
PeteRH

[tubedogsmith]

This amp has more bottom end than an AC30 and the top end is smoother, more hi-fi sounding. I get my chassis' made up by a sheet metal shop. They do all the holes with a laser and mount the threaded rivets. I have a brake and have made a bunch of chassis' myself but I hope I never have to again!!

[Mark]

Dear Tube Dog Smith

Thanks for the description of your amp. I have played some AC-30's that were very clean sounding. Grey panelled amps usually.

I have once played a copper (red) panelled AC-30 (which I loved) and I thought the Rocket reminded me of that particular amp.

That copper panelled amp that I played didn't stay clean as the grey ones did, it had this great break up which I loved. The amp didn't have as much gain as an Express/Liverpool or possibly a Mesa Boogie Mk 1, but it didn't lack gain and I didn't have any problem coaxing the amp to feedback.

It sounded best with humbucking guitars while the the Rocket prototype amp seemed to prefer single coil guitars such as my Strat.

Again, nice work.

[keithrick]

Hi Tubedogsmith, I have a few question if you don't mind regarding your build. As you can see in my new thread that I have started my own Rocket inspired amp.

These questions are based upon your pic posted in this thread and the schematics in the files section.

1. I believe you are using the plate resistor value of 220K for V1. Are you also using 1.5K as the cathode value or 3.3?

2. I am assuming V2 pin 6 that goes to the board is connected to B+4? and powers V2 pin 1 through the 100K resistor?

3. What is you value of the bias resistor on your board? It looks like 820 ohms 10 watt? The schematic in the files section states 50 ohms and the PS board in another post lists 130 ohm.

Thanks in advance for any help. If you have any soundclips please post them!

[tubedogsmith]

220k plate resistor and 1.5k cathode on first stage
Right on the plates for V2
62ohm cathode resistor on output tubes
V2 uses 1.5k and 68k cathode resistors

[UR12]

These questions are based upon your pic posted in this thread and the schematics in the files section.


3. What is you value of the bias resistor on your board? It looks like 820 ohms 10 watt? The schematic in the files section states 50 ohms and the PS board in another post lists 130 ohm.

Keith

130 ohms is for 2 EL84s and 50 - 65 ohms is for 4 EL84s. Since you have twice the current flowing through your bias resistor with 4 tubes compared to 2 tubes you have to halve the value of the Cathode resistor to get the same voltage drop (Bias).

The schematic you are refering to using 130 is the ginger schematic with 1/2 power switch. In this configuration each pair of El34s have their own cathode resistor so that two tubes can be switched out and the other two left running .

[keithrick]

Thanks Tubedog for listing the values. I have been examining your amp pic and related posts as well as Paul Ruby's "Diana," and Mark Abbotts schematics and layouts trying to fully understand the design before actual assembly.

Dana, thanks for clearing up the 130 ohm (2 el84's)and 50-65 ohm (4 El84's) bias resistor issue for me. I do intend to use a half power switch. I need to visit Mr. Aiken's site to read up on cathode biasing.

[utervo]

Hello everyone it's my first post!

I was wondering what the PSU configuration is?

[rfgordon]

Beautiful work. I can't wait to hear clips, if they're forthcoming.

I'm fixin' to audition a new brand of iron, and was gonna make a 5E3 sorta thing, but now I'm thinkin' maybe a Rocket-inspired 6V6 amp. A colleague of mine at work (sometimes it's great to be a nerd among nerds) just bought "several hundred" tubes from the widow of a recently departed TV repair man. I got a batch today, used but good 6V6s, 6K6s, 12AX/AT/AU7s, 5U4s. He has yet to go thru the NOS stuff--drool, drool. So I'm thinking I need a vehicle for some of these nice vintage tubies!

You guys just feed my sickness...

[Beerman]

Beautiful work. I can't wait to hear clips, if they're forthcoming.

I'm fixin' to audition a new brand of iron, and was gonna make a 5E3 sorta thing, but now I'm thinkin' maybe a Rocket-inspired 6V6 amp. A colleague of mine at work (sometimes it's great to be a nerd among nerds) just bought "several hundred" tubes from the widow of a recently departed TV repair man. I got a batch today, used but good 6V6s, 6K6s, 12AX/AT/AU7s, 5U4s. He has yet to go thru the NOS stuff--drool, drool. So I'm thinking I need a vehicle for some of these nice vintage tubies!

You guys just feed my sickness...

Hey fella.

Have you seen Mark Huss' Plexi 6V6? Something like that might be worth a look too. Check it out at www.mhuss.com

Cheers

g

[utervo]

I am still wondering what power supply that is?

I read somewhere it had an AC30 choke?

To build a 2 x EL84 Rocket, what changes can/are to be made?