Anybody try the Hammond Vox choke?

[rooster]

I'm looking at the Rocket/AC30 choke and I run what most of you here run, the Hammond 158L. This is 15 H and has a DC resistance of 411 ohms. On the other hand, the Hammond made Vox clone is rate at 30 H and has a DC resistance of 517 ohms, +/- 15%.

Has anybody here tried both of these chokes? Thoughts?

[rooster]

Haha, OK, I'll take that as a 'no'. But not to be deterred, I have ordered the Hammond Vox choke and will receive and install it this coming week. Having worked on maybe ten vintage AC30s over the years and having built more than a few Rockets, I just have to know how this one element might change things. Sure, there's speakers, but there's also that choke.

[M Fowler]

No I use the 158L and in my Tino Zottola Book Volume 2 building Vox ac30 top boost he notes to use a choke with 10H 100mA.

Vox must have changed to that 30henry choke later?

Mark

[M Fowler]

On my Zwreck clone I did use a Hammond 159M 15h, 100mA, 256vdc choke.

[rp]

I never built either, yet. Half built Rocket on a shelf. I'd worry my Rocket would sound too much like an AC30, which it is 99% circuit-wise, it's only a few values in the power string that make it different. I will build it exactly like the TAG schematics and see what I get, then if I don't like I can always soften it up into an AC30 it. I chose the Rocket for that reason (and that 15,000 TAG members can't be wrong) but just in case they are. An AC30 if a known quantity to me and it's always nice to have an AC-30 on hand. If I can find one I'll try the 80mf as first cap too as I have a couple real Mullards on hand. That 80mf makes no sense whatsoever unless KF really had to have it.

[M Fowler]

Ken F. used the Stancor C-1002 which is the Hammond 158L.

The TW Rocket amp named Jovanna used a Hammond choke.

[rooster]

Hey guys, thanks for speaking out. I do like the Rocket circuit, yes, but then there's all these AC30s that have come through here for repair (and fun, too!). And there's something about them that is different. Most ppl will say it is the vintage speaker that makes for the difference, and Ken did have use of a pair of silvers (belonging to Chris Merren), and a pair of blues that he loved, in two different cabs.

OK, and now here's an update because I did receive the 194E Hammond choke today and install it. It is built to Vox vintage specs so it is much larger and heavier than the 158L, BTW. It measures 507 DC ohms resistance and is 30H.

I know it takes a while to settle, being a transformer, but let me report on the first hour and my first impression. It is different sonically, no doubt. It actually seems to add that AC30 'roar' thing that the Rocket has a bit of but not quite as much. I'm thinking it is adding bass and low mids, which some might not like, and also a slightly different feel. (I don't want to commit to the feel thing right now because this is one thing I was pretty sure would happen - and I may be biased about it/it could all be just sonics.) For now, I perhaps can see where Ken would say that he was not cloning an AC30TB, but instead creating something different. That said, it's weird to think that a change in choke could be the major contributor to his new design.

These findings may change after a few hours or days, so I'm just getting this out. This was all with a Tele using a Timmy pretty much.

[RJ Guitars]

I had to dig a bit to find my notes and photos on this... I have a note from a guy that bought parts from me to clone his original Rocket.

Here is what he had to say: "... it sounds very nice. More bass than I expected even though it's the same the circuit as the original. One thing I can't figure out is that now I am getting a 7 volt drop across the choke whereas on the original it is a 2 volt drop. Do you think that maybe Ken used a different choke on the original. I've seen where people say that the originals had a choke with a 400 ohm rating but the 2 volt I measure would imply there is only about 100 ohms on the choke."

This is something interesting to contemplate since it is the only actual voltage measurements from a real Rocket that I have had access to. The choke does not look like the Hammond 158L. It doesn't have a plastic bobbin but looks more like an old paper wound unit on a similar core size. It has been painted flat black and had some hand lettering on it that said something like "Skull XXX XFMR". I would not be surprised to learn that this was a unique hand wound unit. Sorry I can't post a photo but it does look very similar to the one on the Amanda Rocket (with the exception of the paint job).

[Roe]

I think that an ac30 style amp needs some screen resistance in order to sound right. Vox used 100 ohm screen resistors and a choke with a DC resistance of roughly 420 ohms. I've tried 110ohms chokes but hated the sound

[RJ Guitars]

That is good to know... I am not really tempted to try anything different since it seems that 400ish ohms is not all that much and the circuit needs to see some resistance there... if my intuition is worth anything?

I have an OEM Vox AC-30 choke here that was made by Dagnall. It measures out at 415 ohms DC so that helps me believe we are in the right ballpark with our various Rocket spec chokes we typically use. IIRC, it is also a 15H choke. I'm not quite sure what the story is on my friends original Rocket though?

[rooster]

Typically the closer the screen voltage vs. plate voltage = louder amp, somewhat brighter/'harsher'/edgier and more aggressive overall.

It is very interesting to hear of a 100 ohm choke in an original Rocket. Big news to me, wow! I'm not sure I would like it frankly, but then there's Ken's ears. Too, I heard that he was trying to make a faster amp at this point, what with polystyrene caps. This may have been an extension of that idea, I dunno. Thanks for the input RJ.