Rocket mods

[Reeltarded]

Looks beautiful!!

[Mark]

Thanks Miles.

[Amwatts]

That's a beauty, Mark. A very clean build. What speakers are you running in that 2x12 and open or closed?

Cheers

Thanks for your kind words.

I’m still working out the speaker situation. I have been using my Marshall 18 watter as a speaker box. It has a Blue and a H30 in it.

In the pic the amp is sitting on a 2X12” cab with Mojotone Greyhounds in it. It’s Barry Marie’s cab and he finds they sound good with any amp.

I had heard good things about a Jensen Neo speaker, but I haven’t made any decisions yet.

https://ampgarage.com/forum/viewtopic.php?f=1&t=36198

That's a stunning amp Mark, I might have to dive into a Rocket one day ,

Barry and I were discussing the Jensens last week, I came across two on Marketplace ... Definitely great sounding speakers for the Fischer circuit , I have one in my Express Deluxe build

[Mark]

That's a beauty, Mark. A very clean build. What speakers are you running in that 2x12 and open or closed?

Cheers

Thanks for your kind words.

I’m still working out the speaker situation. I have been using my Marshall 18 watter as a speaker box. It has a Blue and a H30 in it.

In the pic the amp is sitting on a 2X12” cab with Mojotone Greyhounds in it. It’s Barry Marie’s cab and he finds they sound good with any amp.

I had heard good things about a Jensen Neo speaker, but I haven’t made any decisions yet.

https://ampgarage.com/forum/viewtopic.php?f=1&t=36198

That's a stunning amp Mark, I might have to dive into a Rocket one day ,

Barry and I were discussing the Jensens last week, I came across two on Marketplace ... Definitely great sounding speakers for the Fischer circuit , I have one in my Express Deluxe build

Barry is still very impressed with the Jensen speaker. It’s in a Deluxe Reverb amp he built which he considers the best DR amp he ever built. I will have to visit and hear the amp. He has my Rocket amp at the moment.

Traditionally, I thought Ken Fischer used Celestion Blues and Vox Silver framed speakers. Who knows what he would use now?

[JD0x0]

I saw the voicing mod in a real Rocket. Ken Fischer installed it. It puts a 22uF cap across the 1.5K (R5) and put a 220K resistor to ground to form a voltage divider with the 220K (R10) going to the P.I. stage.

https://ampgarage.com/forum/download/file.php?id=8003

I don't understand how this would add a mid cut for humbuckers, as described earlier in the thread. The 22uF across R5 would increase gain at all audio frequencies, while the 220k/220k voltage divider would cut ~50% gain pre-phase inverter. Seems like it'd add the potential for more preamp distortion, while taming the gain hitting the PI a bit, to compensate. Basically, it's like turning the preamp gain up, while turning a pre-PI master volume down, a bit.

[Mark]

I saw the voicing mod in a real Rocket. Ken Fischer installed it. It puts a 22uF cap across the 1.5K (R5) and put a 220K resistor to ground to form a voltage divider with the 220K (R10) going to the P.I. stage.

https://ampgarage.com/forum/download/file.php?id=8003

I don't understand how this would add a mid cut for humbuckers, as described earlier in the thread. The 22uF across R5 would increase gain at all audio frequencies, while the 220k/220k voltage divider would cut ~50% gain pre-phase inverter. Seems like it'd add the potential for more preamp distortion, while taming the gain hitting the PI a bit, to compensate. Basically, it's like turning the preamp gain up, while turning a pre-PI master volume down, a bit.

I hear what you say. I didn’t expect that result either, but that’s what I experienced. I like it for humbuckers though.

[Fischerman]

I built a Rocket and then later a Z-Wreck. The Rocket sounded better but it was not the circuit per se. I tried all sorts of things (making it more and more Rocket-like) and never got the Z-Wreck to sound as good as the Rocket. Even after it was essentially a Rocket. Sold it.

Then it dawned on me that I never went the other direction and never tried any of the Z-Wreck differences in my Rocket. I ended up with the 22uF cap on V2 cathode and the extra 220k to ground at PI input. I later saw that Matchless amps have those same mods except a 220k/100k divider instead of 220k/220k divider at PI input and I like that a little better. Minor tweek.

I also doubled up V1 (parallel triodes) using a 100k plate and 1k cathode resistor, same 22uF cap.

[Fischerman]

First time I recapped one of my own builds. I originally built this with old caps I had on hand and they were only rated for 350v. Fine if you don't power up the amp without tubes but probably not if you did (I never did). Took me this long to get around to doing it right. This is more like a Matchless power supply. Posting it along with the voltages which are higher throughout. Except for the screens which are lower. My cathode voltage when connecting the screen grid resistors to the choke was about 10.45vdc across a shared 56ohm resistor. With the new power supply (same tubes) it is 8.57vdc.

Node is not used except as a branch off point. B+2 is the screen node.


More DC-30 than Rocket anymore. V1 triodes run in parallel, 110k/820R/22u and 1000pF coupler/500k vol.

[gktamps]

Definitely higher voltages, but should sound nice. Does it?
Have you played with bumping up the screen voltage a bit, or are you satisfied as-is?
Looks great!

[Fischerman]

Definitely higher voltages, but should sound nice. Does it?
Have you played with bumping up the screen voltage a bit, or are you satisfied as-is?
Looks great!

Thanks. I think It sounds bigger and more full. With a little more available gain but more noticeably less compressed. I think it sounds great. I recently built a 15W Lightning clone and it sounded every bit as big as the Rocket. So that got me looking into it. The main reason I went to the trouble of doing it this way was to be able to dial in the screen voltage. This was my target, right at 12W per plate. I'm using Russian 6n14n which are technically 14W tubes but I wanted it setup for 12W EL84s. I 'scoped it before and after and before there was no crossover notch that I could see but after there is a tiny, tiny notch.

My guess is that maybe running it so hot at idle, there wasn't anyplace to go when you actually asked it to make sound. So it sounded too compressed. I was surprised that after this mod the cathode voltage only went up to 10.1vdc at max output. I was running it at 10.45v idle cathode voltage. EDIT: if you look at the Ceriatone Lightning power supply, Nik uses a 2k2 dropping resistor for the screen node. I tried it on my Lightning but it was too high. My Lightning has a 10k resistor instead of 4k7 and has almost the exact same voltages on the plates/screens.