Rocket Power Transformer Story - Revisited

[RJ Guitars]

Hello Folks,

I know, I know - we've been through this, but recently I've come across some additional info that has me convinced we've not yet uncovered the whole Rocket transformer story... I'll begin with only the power tranny, believing that the output tranny may deserve a thread all it's own.

Heyboer
PT HTS-9144
OT HTS 8093-1
CH Hammond 158L

For many years, this has been the gospel of transformer knowledge concerning the Rocket... it has worked out well for lots of amp builds. I'm not sure if it's wrong, but I am beginning to believe it is not entirely complete.

The Rocket Jovanna has paper wrapped Stancor choke C-1002
75mA, 400 ohms DCR and 15H.

The OT in Jovanna is a dynaco A-470-s.

Another PT used in Rocket was the Stancor P-8356 270-0-270 (260mA), 5v3A, and 6.3v/8.8A

The amp reported to be a JM build (see pictures) does not strickly follow the lead dress and color code of an authentic TW Rocket... but could be legit, I just don't know for sure. I was just beginning to grow skeptical that this was not a real Wreck build when that odd little 5v tranny has again showed up in a more recent revelation that I was provided.

I have recently seen inside another authentic Rocket amp and it uses a Pacific power tranny and the 5V transformer inside the chassis much like the above mentioned amp. As another matter of interest, it uses the chicklet coupling caps.

I don't know how many of you have seen the original Rocket gut shot that has floated around here for years but does not show the actual power supply. Until now I am not fully convinced I've seen one before.

Now lets jump to another piece of folklore. Rocket #1 and #2 are said to be powered with the Stancor P-8356 that is mentioned by Master Fowler above. I cannot confirm this but the story has been told a time or two but folks that ought to know.... but in the last half hour received a report that this was another red herring?? It's hard to say...

All of these stories would totally change the reported voltages we are familiar with in the Rocket amp - YMMV?

rj

[Zippy]

I know, I know - we've been through this, but recently I've come across some additional info that has me convinced we've not yet uncovered the whole Rocket transformer story... I'll begin with only the power tranny, believing that the output tranny may deserve a thread all it's own.

Heyboer
PT HTS-9144
OT HTS 8093-1
CH Hammond 158L

For many years, this has been the gospel of transformer knowledge concerning the Rocket... it has worked out well for lots of amp builds. I'm not sure if it's wrong, but I am beginning to believe it is not entirely complete.

The Rocket Jovanna has paper wrapped Stancor choke C-1002
75mA, 400 ohms DCR and 15H.

The OT in Jovanna is a dynaco A-470-s.

Another PT used in Rocket was the Stancor P-8356 270-0-270 (260mA), 5v3A, and 6.3v/8.8A

Now lets jump to another piece of folklore. Rocket #1 and #2 are said to be powered with the Stancor P-8356 that is mentioned by Master Fowler above. I cannot confirm this but the story has been told a time or two but folks that ought to know.... but in the last half hour received a report that this was another red herring?? It's hard to say...

All of these stories would totally change the reported voltages we are familiar with in the Rocket amp - YMMV?

rj

Good stuff (as always), RJ. Your scholarship in this area is superb.

Could you please, for the sake of comparison, post the specs for the Heyboer?

What B+ voltage ranges are reported for the various known Rockets?

If you'd rather PM a response, that's fine.

[Drew.12345]

RJ,
Your quest for TW knowledge and inisight is truly admirable.
I have just finished up my Rocket build and used a Stancor 8356 PT.
My voltages were a little higher than I expected and I had to adjust my bias to bring it back into spec.
I used a MM Dynaco OT as well as the reccomended Hammond 158L choke.
I had to substitute a 68 ohm bias resistor in favour of the 50 ohm to get my tubes from redplating.
By my calculations I am running the El84's at 13w @42ma.
I took some voltages and thought I'd share them.
I measured my wall voltage before and after testing to ensure they stayed consistent at 116.8 v.

5AR4
Pin 2/8 = 333v
Pin 4/6 = 277AC

EL84 V4,V5
Pin 3 cathode = 11.9v
Pin 4 heater = 3.2
Pin 5 heater = 3.21
Pin 7 plate = 324v
Pin 9 = 319v

EL84 V6,V7
Pin 3 cathode = 11.9v
Pin 4 heater = 3.22
Pin 5 heater = 3.22
Pin 7 plate = 323v
Pin 9 = 319v

Here are some pics.

[RJ Guitars]

I've started a spreadsheet on Wreck power trannies that I'll add to this thread later and I will include the Heyboer Zippy mentioned as well as some off the other popular choices for Rocket builds.

The real fun here is to get a look inside a Rocket and find a couple surprises. The 1st is to see the familiar Pacific power tranny and the 2nd is to see the independent 5V tranny inside the chassis. I have a note from Pat Thomas (one of the founders and CEO of Pacific tranny) indicating that they only designed and built one set of transformers for TW. I sorta assumed this meant that they didn't make the Rocket PT.... What I didn't expect was that TW would use the familiar Pacific power tranny (Part#11410) and add an external 5V transformer.

Concerning the use of the 8356 tranny - I can't find any support for it being an authentic Rocket power tranny but Drew's build report makes it clear for us that it's a great choice for a Rocket.

If the early Rockets use a similar voltage to the 11410 Pacific power tranny then the Stancor P-8378 would be more similar but at this point that common element is just a coincidence, not supported by any real evidence that I have available to me.

In the earliest days of cloning the Rocket amp there was a maximum B+ of something around 305 volts on the output tube plates. In every photo and report of the Rocket power supply (including this latest Rocket that I've seen into) the same dropping string was used - Starting out of a GZ-34 tube rectifier going into the first filter cap into a 400 ohm (DC resistance choke) and then into the familiar series of resistors - 18.2K / 9.1K / 9.1K. Only the transformers seem to vary. I'll leave this for now and start hunting down voltage info from the TAG archives...

[RJ Guitars]

I have just finished up my Rocket build and used a Stancor 8356 PT.
My voltages were a little higher than I expected and I had to adjust my bias to bring it back into spec.
I used a MM Dynaco OT as well as the reccomended Hammond 158L choke.
I had to substitute a 68 ohm bias resistor in favour of the 50 ohm to get my tubes from redplating.
By my calculations I am running the El84's at 13w @42ma.
I took some voltages and thought I'd share them.
I measured my wall voltage before and after testing to ensure they stayed consistent at 116.8 v.

That is excellent to have this info. It would seem that your need to change the cathode resistor does tend to eliminate this power transformer as a standard value for a Rocket build... although didn't VOX get by with similar voltages in the AC-30 and kept the 50 ohm bias resistor - am I missing something?

[RJ Guitars]

I want to throw out one more quote from the history archives to maybe help tie the pieces together and some of them confirm what we're seeing in these more recent days...

...I compared the sound with two people's amps (real wrecks) and it is the same. It is of some importance to note that one of the guys has modded his real Rocket to the higher taps and higher cathode resistor to get more "Girth" out of his amp. The other chooses to keep his stock for the incredible jangley cleans.

[RJ Guitars]

Here is another quote from a more recent thread... ampgarage.com/forum/viewtopic.php?p=274307

Yes, it looks like a JM trainwreck reissue. The transformer inside to drive the rectifier tube heaters is something that Ken used in the past in another rocket....

This agrees with what I've seen recently... gives me a little more of a warm fuzzy to know that someone else has seen it and mentioned it before me. It's starting to clarify the picture a bit but I am puzzled why KF wouldn't have pursued the development of a PT with a 5V tap... any thoughts?

[redshark]

Very interesting!!!! All we can have about this are assumptions but here is how I think things could have happened.

Original trainwreck transformers were P-8378 PT and A-8301 OT.

In the late 80's the pacific parts 11410 PT and 11415 OT started being used. 11410 has same specs as P-8378 but without the 5V tap. At that moment not really a need for it because both available trainwrecks Liverpool and Express didn't use a rectifier.

The rocket was built for the first time in 1990 and maybe still Ken had a few P-8378s that he could use or maybe another stancor PT 250-0-250 with a 5V tap could have been used too.
In case of using a pacific PT he also needed to use that filament transformer to get the 5V for the recto.
I think also in the early 90's Ken started to experiment with transformers and it has been documented a rocket with a Heyboer PT (I think only 1).

I think probably around 8-9 rockets were built by Ken so what OT's were used? I'm sure variations by Chris Merrin were built for this.
The facts are that the rocket is based on VOX AC30 and VOX used diferent transfomers so with the dynaco A470 also in the picture there was room for a lot of experimenting....

All of this my assumptions.....

[rp]

...although didn't VOX get by with similar voltages in the AC-30 and kept the 50 ohm bias resistor - am I missing something?

That they were unreliable?

[2tone]

Very interesting!!!! All we can have about this are assumptions but here is how I think things could have happened.

Original trainwreck transformers were P-8378 PT and A-8301 OT.

In the late 80's the pacific parts 11410 PT and 11415 OT started being used. 11410 has same specs as P-8378 but without the 5V tap. At that moment not really a need for it because both available trainwrecks Liverpool and Express didn't use a rectifier.

The rocket was built for the first time in 1990 and maybe still Ken had a few P-8378s that he could use or maybe another stancor PT 250-0-250 with a 5V tap could have been used too.
In case of using a pacific PT he also needed to use that filament transformer to get the 5V for the recto.
I think also in the early 90's Ken started to experiment with transformers and it has been documented a rocket with a Heyboer PT (I think only 1).

I think probably around 8-9 rockets were built by Ken so what OT's were used? I'm sure variations by Chris Merrin were built for this.
The facts are that the rocket is based on VOX AC30 and VOX used diferent transfomers so with the dynaco A470 also in the picture there was room for a lot of experimenting....

All of this my assumptions.....

Rockets had different power trannies. Mine was made by West I believe. Ken tried different ones out. Mine has the two voltage taps, and I'm the one that converted to high voltage for more muscle etc.

[RJ Guitars]

Very interesting!!!! All we can have about this are assumptions but here is how I think things could have happened.

Original trainwreck transformers were P-8378 PT and A-8301 OT.

In the late 80's the pacific parts 11410 PT and 11415 OT started being used. 11410 has same specs as P-8378 but without the 5V tap. At that moment not really a need for it because both available trainwrecks Liverpool and Express didn't use a rectifier.

The rocket was built for the first time in 1990 and maybe still Ken had a few P-8378s that he could use or maybe another stancor PT 250-0-250 with a 5V tap could have been used too.
In case of using a pacific PT he also needed to use that filament transformer to get the 5V for the recto.
I think also in the early 90's Ken started to experiment with transformers and it has been documented a rocket with a Heyboer PT (I think only 1).

I think probably around 8-9 rockets were built by Ken so what OT's were used? I'm sure variations by Chris Merrin were built for this.
The facts are that the rocket is based on VOX AC30 and VOX used diferent transfomers so with the dynaco A470 also in the picture there was room for a lot of experimenting....

All of this my assumptions.....

Seems like a reasonable assumption and well supported by what we are seeing.

I assume that is a typo on the A-8301 and you really mean A-3801...

I have talked about building the ultimate AC-30 with Chris Merrin before and he gave me some transformer thoughts to mull over. Firstly, he doesn't want to lean on or market his connection with Trainwreck in any way. He was really clear that he didn't want to make any money from Ken Fischers work... then we got down to talking about transformers and AC-30's. He defined a sweet spot in the AC-30 tone with a B+ of 305 to 310 volts when combined with an impedance of 3.7k to 3.9K on the output transformer. There was a very clear connection in finding the sweet spot based on this relationship of values. I am not saavy enough to sort this out in my head but suppose it could be done mathematically to verify and understand why this would be true. Up to this point I was thinking that the amp might benefit more from a slightly higher OT impedance... but based that mostly on KF's preference of a higher impedance OT for his high gain amps. Any thoughts?

[RJ Guitars]

I've started a s spreadsheet on Wreck power trannies that I'll add to this thread later and I will include the Heyboer Zippy mentioned as well as some off the other popular choices for Rocket builds.

The real fun here is to finally see inside a Rocket and find a couple surprises. The 1st is to see the familiar Pacific power tranny and the 2nd is to see the independent 5V tranny inside the chassis. I have a note from Pat Thomas (one of the founders and CEO of Pacific tranny) indicating that they only designed and built one set of transformers for TW. I assumed this meant that they didn't make the Rocket PT....

[Paultergeist]

I realize part of the challenge here is to unravel the mysteries of the past, but I just do not see any real advantage to the internal 5V transformer.....

Can anyone think of any rationale as to why this may benefit the amp......other than perhaps the PT on hand at the time simply did not have 5V taps for the rectifier?

[redshark]

I realize part of the challenge here is to unravel the mysteries of the past, but I just do not see any real advantage to the internal 5V transformer.....

Can anyone think of any rationale as to why this may benefit the amp......other than perhaps the PT on hand at the time simply did not have 5V taps for the rectifier?

It wasn't about a benefit to the amp. It was just about powering a rectifier. That's it!!!

[RJ Guitars]

I really like unraveling the puzzle, it's cool to make sense of another piece of the history. It's also a telling factor in understanding not just how Ken Fischer did things, but why. In this case the why is probably because he was using what he had around. He was famous for doing that but this was not something I would have ever suspected.