Vintage AC15 versions Big choke vs little choke

[chopstuck]

I came across a big AC15 choke from my man at Heyboer. Its about 10H at 150 ma. I have a few ac inspired amps to fool with but I was thinking of doing a real retro AC15 with the wonky trem.
I have a couple of grey panel ac30s that sound great when the decide they want to. The trem somehow contributes to the sound as per the Tone Lounge lizard man. I have to agree as not even a rocket compares to them.
I have a regular six input non top boost and a super reverb twin head. Different animals but both great.

I just got my tweed Super/ Bandmaster clones sounding killer with the correct size chokes and OT's.

Now I think it may be time to try running my Vox plates after the giant choke on B2.
There was some kind of magic there with the tweeds PS when the right parts were used and the voltages finally came into line.

Anyone try the two chokes on a similar circuit ?

[diagrammatiks]

I don't know the formulas for choke current requirements off the top of my head...

I'm assuming that you want to run a capacitor reservoir choke then another capacitor to ground instead of a choke input filter?

If you run a resistor right after the reservoir before the plates that resistor usually needs a pretty big wattage...

I think the choke is ok as long as the current it is rated for is greater then the draw of the amp.

[chopstuck]

The big choke schematics are at schematic heaven as the 1959 and 1960 ac15's .

Here

http://www.webphix.com/schematic%20heav ... 151960.pdf

and here

http://www.webphix.com/schematic%20heav ... 151959.pdf

[diagrammatiks]

It looks like they take the plate and screens from the same node in those schematics.

so you get the big filter choke before the first b+ node but you lose filtering between the plate and screens.

That's interesting that they did it like that. I wonder what the sound difference would be.

[chopstuck]

Me too. It's what the late tweed Pro, Bandmaster and Super did.

I made the change from small choke between the plate and screen to the big choke ahead of both and the amps came alive !

The "oversized" choke on the plates and screens set up a change in the PS that just made it sound compressed and "Tweedy" where it just sounded like plain blackface tone before.

[Roe]

putting a big choke before the OT like a 5e1 gives better filtering and tighter bass (compared to a circuit w/o this choke, e.g. 5f1).

[chopstuck]

Thanks Roe, that's the kind of info I'm searching for.

[rhinson]

i've built several ac30's with the "brute force" front end (cap-choke-cap) with some chokes i had heyboer make for me 7h/300ma. brian may's amps were changed in this fashion. it allows you to use the lower filtering (and have that kind of feel) without all the ghosting that comes with lower filtered amps from back in the day. it's the tweed twin or ac15 approach essentially. it like it quite a lot. rh

[chopstuck]

Wow, 7H at 300ma - That's a big choke
What would one run roughly $?

Do people who know the AC30 sound notice this right away ?

[diagrammatiks]

you can get a choke that big for like 50-70 bucks.

[rhinson]

it's not that large size wise----i think it's the same open frame size as a pro/bandmaster/18w marshall output trannie but with a bit thicker stack. i'll post my heyboer part number when i get home and you guys can feel free to order some. i bought a batch, but i believe they were about $30ea as onesies. rh

[Roe]

any source for big chokes like that? I'd like a 250ma+ one for an ac30 and a 500ma+ one for a 100w

[rhinson]

the part number for the ones i had heyboer make is hts-6607
if you do a search for brian may and dave peterson you can find the big pdf file on his mods (somehow my browser won't load it anymore)

also aschematic is on greg fryer's site---he was involved as well

http://fryerguitars.wordpress.com/2009/ ... i-version/

it is slightly different than the original dave peterson thing you can find on mike ryde's site (the big pdf file) rh

[chopstuck]

Rhinson, thanks for the link.

A few years ago I built a quick and cheap Spitfire/18watt on an old AO-35 chassis with a preamp triode single / parallel switch and no choke.
It was largely lifted from Ken Watts site.

I ended up just liking just the single triode. I felt silly because it was my favorite go-to amp for years.
Just volume and (tone wide open). (I had also replaced the OT with a TDS 15W Matchless spec.)
Now that idea has gone mainstream with the one knob AC30 .
I feel validated.

I suppose next I will try a 15 watt version of the BM amp since I have most of the big pieces.

Also I think maybe I will try your big choke idea on a Stang Ray clone I built in an old Lafeyette amp.
That one was built to the ac30 schem and I just thought it sounded too hi-fi. Hmm- I should check the OT primary impedance for Hi-Fi ness.

Thanks again for your input.

Marc

[chopstuck]

Found the PDF site here.

Lots of great info, including WHY Brian may had that wall of AC-30's

http://www.mikeryde.com/%5CDP_Amp%5CBMA ... P_Spec.pdf