rocket choke

Express, Liverpool, Rocket, Dirty Little Monster, etc.

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phillyhudson
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rocket choke

Post by phillyhudson »

hi all,

starting a rocket build and am using the same set of trannies I had built for express but now need a choke - loath to cough up for one if I dont need to , so just wondering how much difference using a hammond 194B [ 4H@90mA out of a twin build ] would be coz I already have one spare ?
ta in advance
phil
redshark
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Re: rocket choke

Post by redshark »

The Express and rocket output transformers aren't the same.
Look on the Rocket BOM for the Hammond model.
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RJ Guitars
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Re: rocket choke

Post by RJ Guitars »

Yep, Red Shark has this correct - they are very different animals.

The Rocket is the Top-Boost channel from an AC-30, but the biggest difference is the transformer set.

If you find a PT that is from 245 to 260 volts on the secondaries then you will be in the right ballpark. You could use a zener diode to make use of a higher voltage tranny and drop the voltage down to where it's typically at - maybe consider one of the new VVR units that are to be available sometime soon (a little hint of something cool that is coming our way) and dial your B+ voltage to where you want it.

For the output tranny there are lots of options but typically they are some sort of variant of a Dynaco 470 HiFi tranny.

The choke in a Rocket is almost identical in specs to an AC-30 choke - 15 Henry and ~390 ohms, although the typical choke used in a Rocket is rated at 75mA where an AC-30 choke is rated at 100mA.

FWIW - I built a Rocket using AC-30 transformers and it sounded great, it sounds very cool but is a bit different from the normal Rocket.
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Roe
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Re: rocket choke

Post by Roe »

the DC resistance of the choke is very important. To[o] low and the tubes won't last long or even sound good
Last edited by Roe on Wed Jun 07, 2017 6:33 am, edited 1 time in total.
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Blackburn
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Re: rocket choke

Post by Blackburn »

Roe wrote: Mon Jun 05, 2017 11:53 am the DC resistance of the choke is very important. To low and the tubes won't last long or even sound good
+1,000

Get the 15H/75mA choke that Hammond offers and call it done.
pdf64
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Re: rocket choke

Post by pdf64 »

If you'd much rather use the TR choke and minimise cost, then I suggest to add some series resistance to it, eg x=3 x 100 ohm 5 watt.
But pentodes do benefit from a well filtered g2 supply, so more inductance (as well as more resistance) is to be preferred.
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Plexified
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Re: rocket choke

Post by Plexified »

I think this is a very good discussion that may be important to expand upon . A schematic for a Trainwreck is just a jumping of point. A good amount of fine tuning went into each amp over the span of roughly a week before delivery. Up to the point that amps were simply destroyed because Ken deemed it cost prohibited to correct. It was simply easier for him to start over.

The choke is one area that has a wide range of tuning depending on what effect you want to employ. In some cases you can fine tune a faster response or lag as Ken refers to slew rates. You can simulate a tube rectifier for example . Plus just the comparison between a choke vs a resistor is significant beyond cost alone. This whole tuning is expanded from materials , layout, and tolerances outside the schematics. It can be compartmentalized like filtering, Transformer design , filtering and frequency in different areas of the schematic. And these are techniques that are developed over time and experience and repairing other amps that become priceless over time.
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Guy77
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Re: rocket choke

Post by Guy77 »

I finished a 30 watt rocket build recently using hammond ac30 power transformer and it also sounded great. The amp was originally a Liverpool using trainwreck express output transformer. I kept this output transformer for the rocket and it sounded good too . I did an ab test with a weber ac30 output transformer and the trainwreck express output transformer from mojotone . This is the one
http://www.mojotone.com/amp-parts/Trans ... ransformer

I actually perfered the trainwreck mojotone one better than the weber ac30 one! I think the weber one is actually made in china..

But what made the biggest difference for me was adding the correct choke to the rocket amp! Wow the amp sounded so much better with the right choke!

I wanted to give a big shout out to RJ and say thank you for all your contributions to this forum.



Cheers

Guy
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RJ Guitars
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Re: rocket choke

Post by RJ Guitars »

You are welcome... the folks in this forum have been really good to me and TAG has been "The" Institution of higher learning through threads like this one.
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M Fowler
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Re: rocket choke

Post by M Fowler »

I normally use Hammond 158L for Rocket builds.

The Dr Z Wreck clone I built I used Hammond 159Q choke 7H 150mA 100R 500v max it seems to be a darker amp compared to a normal Rocket.
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