A Rocket (or Liverpool) with 7189s?

[Marcel Bagnole]

Hi, folks, first post here. I have an old Fisher stereo amp that has some problems but has good PT and OTs. I can't find a buyer for it so I am considering building something with it - probably multiple amps, given that there are two OTs here.

Anyway, it occurred to me that I could use the PT with an appropriate OT to build a mono 4x7189 Trainwreck and I thought I'd ask to see if anybody had any thoughts on this. These are interesting tubes - in the Fisher they use a voltage doubling power supply and according to the schematic run 390 volts on the 7189s - far more than you would want with EL84s. A pair of these pushed hard should produce 25 watts and 4 of them double that. What it would sound like I have no idea...I'm sure these voltages are way higher than a Wreck, but the tubes can take it.

Anybody have any thoughts on this?

Thanks in advance.

[Zippy]

There have been quite few octal Rockets that indicate that your idea is a solid way to go.

https://tubeamparchive.com/viewtopic.php?t=7300

A Liverpool/Express build is a lil' more daunting in that the design more close to the cliff of stability - not recommended if you are new to this game. The Rocket is a friendlier build and a very musical amp.

Be sure to scale the power supply dropping string to get recommended voltages in the preamp and phase inverter and you'll be fine - fine and loud!

Enjoy!

[Marcel Bagnole]

Thanks, Zippy. I've built nine or ten amps so am not completely new to the game, but I have been out the loop for some time and am having to get up to speed. That thread is interesting, but it's going to take me a while to get through it - it's a long one. The Rocket doesn't seem to have anything especially daunting in it; in fact, I built a 2-EL84 amp several years ago that was quite similar to it. I've never done a four power tube amp, but I don't see how it would be that different. The preamp and PI design seem pretty familiar if you're used to looking at Tweed Bassmans and Marshalls.

I'm hoping somebody has had hands-on experience with the 7189s; they would seem to be hot rod EL84s but so far I have only heard them in stereo amps.

[Bob S]

I've tried 7189's in a Liverpool (around 375 - 380v on the plates) & it sounded great.
Like Zippy said, you might need to adjust the dropper string a little.
The Russian 6P14P's are also like 7189s - they can take a beating.
It will be LOUD.

[Marcel Bagnole]

I've tried 7189's in a Liverpool (around 375 - 380v on the plates) & it sounded great.
Like Zippy said, you might need to adjust the dropper string a little.
The Russian 6P14P's are also like 7189s - they can take a beating.
It will be LOUD.

EXCELLENT, Bob! Thanks!

[ampgeek]

I went on an EL-84'ish binge a few months ago in preparation for an upcoming build. (I continue to be a tantric amp builder )

Ended up with a NOS matched pair of 7189, a quad of the ruskies mentioned above and a pair of NOS Mullard EL-84s. Can't remember the 7189 manuf. at the moment unfortunately.

I borrowed a friends Blues Jr and plugged it into a 1X12 oval backed cab with a Scumback speaker and played each pair for an hour or so with frequent swapping in different pairs. Trying to do the A/B (C) thing the best that I could.

After all was said and done, I would have been really, really hard pressed to say that there was any significant sonic difference between any of the pairs that I tried.

If I had to pick one that I liked the best, I would have to say the ruskies. More a "feel" kind of thing over any kind of tonal judgment. Not sure how to describe it really. They just seemed to more dynamically match my playing style (e.g., pick attack for break up as an example) is probably the best way to put it.

Cheers,
Dave O.

[Reeltarded]

I borrowed a friends Blues Jr

Cheers,
Dave O.

It lasted an hour?

lol sorry, I am at odds with modern Fenders. Whew..

carry on!

[Jana]

Reeltarded, It was one of the good ones.

[Reeltarded]

[M Fowler]

Dr Z has been using the 7189 tubes in his builds for a while now.

Mark

[ampgeek]

LOL! And that was an hour with each pair of tubes. I guess that my personality really is tragically tantric!!

Truth be told, I didn't sound at all bad going through a different cab/speaker. Really nice pushed blues tone. The stock speaker/cab wasn't to my liking though.

Dave O.

[Marcel Bagnole]

Well, I am interested in 7189s running at higher voltages - I don't think there's much to be gained from using 7189s in regular EL84 amps beyond tube longevity (not neglible, I know). But the 7189s can put out significantly more wattage than the EL84s if the amp can give them the voltage and current to do it. Not that it would be an earth shaking difference; 25 vs 18 isn't much at all. I doubt that you could even hear it; what does that work out to, one dB?

I think that an amp that's built to take advantage of the 7189s would eat EL84s like crazy.

I'm going to build a 4x7189, the question is which way do I go; do I build something that tries to go the clean route or do I dirty up and go Trainwreck? I'm definitely leaning towards the Trainwreck. The Rocket looks pretty easy to make, actually; the Liverpool seems more problematic, appears to have more gain and (I suspect) more issues with instability. I wish there were more clips of Liverpools so I could listen to a wider selection.

[guitardude57]

I have an old Pioneer tube amp, very close to the one you have.
The OT's are very nice and stout, and run 7189's... stereo.

I gutted the thing years ago, and have used it for different amps as a test bed of sorts. Fender, Marshall, etc... amps have lived in there point to point, and mono. I haven't messed with it for a while. I have the left channel OT around here somewhere...

It has been an Express up to now with a twist. I installed a couple of octal sockets, so the amp runs either 7189's, (or pull them out) and 5881's... whichever are plugged in. All the power tubes are cath biased for sake of ease, and a little less power.

The amp sounds decent with either power tube set up, to about 2:00 on the volume, then the blocking starts up. I used traditional value components, with the PTP build and the PT on a doubler seems to run short on current, or oscillation, or both.

At 12:00 volume, it is way loud and clean to mean. I brought it to a jam a couple years ago, and it easily more than kept up with 2 other guitars, a very loud bass player... and a hard hitting drummer.

They were like "wtf is that"? Pretty funny sustaining about any note on the neck, then rolling back the guitar volume into a fender-like clean...


My old (2002) Blues Jr was converted to the Marshall 1986 circuit. A drastic improvement. I hated the original... love it now.

[guitardude57]

Marcel,

Could you give me the secondary wire colors on the OT wiring on your amp?

I believe our OT's are the same (4-8-16 ohm).

I don't remember which one mine is wired to, the speaker jack. Could explain some imbalance that may be there.

Thanks, Mike

[Tyrannocaster]

Marcel,

Could you give me the secondary wire colors on the OT wiring on your amp?

I believe our OT's are the same (4-8-16 ohm).

I don't remember which one mine is wired to, the speaker jack. Could explain some imbalance that may be there.

Thanks, Mike

Hey dude, this is Marcel Bagnole (I was having trouble logging in with the right name so I had a second account for a short time). Sorry, I didn't see your post until today. Anyway, the Fisher OT's wires are:

Yellow 16 ohms
Green 8 ohms
Black Common
(No 4 ohm tap)