SE Rocket build - The Wrong Horse Amp

[Synchu]

I was a bit out of the amp building (besides few tweaks, conversions and repair jobs) in the last year or so due to a lot of other stuff happening around, but couldn't stand the itch anymore.

A friend of mine gave me some time ago (ok a long time ago) a project chassis from a Tweedle Dee that was punched pretty much everywhere with a couple of old radio transformers (built somewhen in the 60s). SE EL84 OT and a non-CT power transformer.

I had a bunch of PCB noval sockets that I wrongly ordered, a wrongly punched Komet 60 power board and wrongly ordered blanket turret board - you get the point around the Wrong in the name. Why horse is a rather long story that I wouldn't bother you with.

That is the amp's description, bullet style:
- quite a bit of filtering at the beginning of the dropping string with a 100uF capacitor, the others are 22uF - experimented quite a bit with various combinations and values and these seem to produce the best sound (to me at least).
- Rocket pre with some adjustments (I have best intentions to draw a schematic- bear with me) and half of the PI
- SE EL84 power amp
- PI half stage is switchable
- switchable voicing of the tone stack
- switchable voltage divider at the power amp entrance (i.e. lowers the signal and amp's volume)

I like the sound best with EL84 biased pretty hot (i.e. 11.5-12W power dissipation) with 335V on the plates.
The power is about 3-4 Watts with 8 Ohm speaker load.

I am having the headshell and faceplate built so these will follow.

To me it sounds great, being or not in the Rocket ballpark

Some pictures:
Fancy a tweak?

Inside:

Outside:

And some sounds. First takes improvisations as always
All guitar tracks are recorded with the amp. No pedals. Somewhat moded Fender Telecaster being used throughout:
Final revision:
https://soundcloud.com/synchu/thewrongkonamp-final-rev
Pre-final revision:
https://soundcloud.com/synchu/thewrongk ... rev-moda-a

Niki

[Synchu]

Finished it with some tweaks around my Telecaster.



And another sample with the Tele. Nice little low wattage amp it turned out.

https://soundcloud.com/synchu/thewrongk ... -tele-rock

Niki

[Guy77]

The amp sounds great! And its only 3 tubes altogether! What microphone did you record the samples with?

Guy

[Synchu]

Thanks Guy,

I'm quite happy with how it turned out.

The sample in the first post was with Beyerdynamic M160 & Gefell M70, the one in the second post is Sennheiser e906 and Beesneez James condenser (it was an open back cab here, so James went at the back).

Niki

[joeboo88]

Nice stuff Niki: great sounds from that little guy.

[drew]

Sounds great. I like spare parts projects like this.

[ChopSauce]

PI half stage: also keeping the 47k resistor?

I tried something like that before (with a 15k cathode resistor & no cap) but the triode was V1B and the amp was picking a lot of noise. One friend says it adds some touch-sensitivity and I agree. Maybe I'll try that on my next build ...
(with a dedicated tube)

[Synchu]

Yep - certainly keeping the 47k.

The half PI adds gain as well (and it makes sense to do so) and quite a bit of it.

I have no noise issues at all, besides some filaments induced hum, since I got 7.3V due to lower load (and PT being purposed for 220V in the old days - now it is 230V - 236V in my particular case).
A 0.56R resistor solved the issue whatsoever and I elevated them a bit soldering the virtual center tap to the EL84 cathode.

Niki

[Synchu]

Changed v2 tube (i.e. third gain stage and half the PI) to 12AV7 and it sounds even better to me, sort of cleaner (expected), fatter and with more defined bass. Very nice.

https://soundcloud.com/synchu/thewrongk ... -the-third

Almost done with the schematic (thanks to a friend of mine who wants a copy of it) and will post soon.

Niki

[Synchu]

Here is the schematic of this build.

EDIT, 27 Nov 2018: Schematic corrected.

SE Rocket EL84s Wrong Horse.jpg

You know the fine print - proceed with caution, consider it a draft, hazardous voltages, etc.

Niki

[fabiomayo]

Hello, Niki.
I built a Champ 5F1 many years ago and was looking to turn into something else and thought this might be appropriate, but with a 6V6 power. My PT can handle the added heater current for a second pre-amp tube.

Have you measured your power supply voltages?

Thanks!

[Synchu]

Hey,

I certainly measured these, however, didn’t bother to write them down. I have now another one of this on the bench as a friend of mine was so thrilled with the sound that he pretty much rushed to build one and it’s here for fixing running.
Apparently, it seems that the heathers winding of the PT is shorted so we will be replacing it.
Once done, I’ll measure and post.
On the top of my head, though, the B+ should be around 300V.
Apologies for the late response, I’ve been out of home for a while.
Niki

[fabiomayo]

Many thanks, Niki. The 300v ballpark is good news.

Let me know if you get to measure this other amp.

Your clips do sound fantastic, by the way!

[Synchu]

It's up and running for some time already, but couldn't find the time to post. They are actually a bit higher than what I remembered.
Here you go (following the PS nodes on the schematic):
A - 350V
B - 345V
C - 213V
D - 209V

Depending on the actual tubes used these can vary, of course. The EL84 is biased at 11.5-12W dissipation. I tend to like JJ EL84 as power output, good quality (Tube Amp Doctor for example) 12AX7 as V1 and NOS (Sylvania or RCA) 12AV7 at V2.

Would be curious to follow, if you decide to build it

Niki

[fabiomayo]

Many thanks, Niki.

I will definitely convert my existing head into a 1x10" combo and will use the opportunity to try the circuit.

It will take a few weeks before I can get started, but will be sure to post.

Cheers and thanks again!