Choke question.

[norburybrook]

I'm thinking of building a BADCAT(Matchless) 30 the EL34 amp. Looking at the schematic it uses a 36H 450R choke.

badcat_hotcat.jpg

Now , I can't find a 36H choke only a 3 or 10H/115R so is there any way round this with an extra resistor or something , or will it do no harm to use the 10H one?


I@m going to use higher value Cathode resistors on the EL34's 360R so the it's not biased so hot.



TIA


M

[Stevem]

Are you darn sure that it's rated at 36 H in that amp, I mean I see it on the schematic, but it's a tad hard to believe!

I ask because it's a huge value and very uncommon and means there's a lot of wire in that Choke!

Where the choke is in that amps circuit ( just regulating the output tube screens and preamp section) and seing that you will have it biased very close to class A I would not go nuts with finding or even having such a choke made since it will not have much effect on the sound and play feel of the amp.

Hammond makes a AC30 reissue Choke, but it's only 30 H which you could go with and it's 100 ma rating is more then enough!

If it where me I would not hesitate in using even a 15H Choke as long as it was rated at enough current and D.C. Voltage, of course other then the real estate needed and the cost, nothing is stopping you from running 2 chokes in series!

One thing I would add during your build to that amp is to put in a 250 ohm 20 watt resistor to ground off of the amps 16 ohm output transformer tap.

This will save your output transformer from a flyback arc over should the amp be played with no speaker load as in one of your series wired 8 ohm speakers going open on you.

[norburybrook]

thanks Steve. I've found an AC30 Choke from Modulus so will go with that. I'll bear in mind the flyback and probably use diodes




M

[joeboo88]

Hi ya Marcus: I built one of these and used a Hammond 194E 30H Choke. I also used Trainwreck Express iron. So it wasn't a true clone
Oh I ended up with 390ohm cathode resistors
This amp has crazy gain but the clean channel is very nice. I sold it as I couldn't dial in a sound I liked.
but that is just me.
I built a AB switcher for this amp, so you can go back and forth

good luck with your build.

[turbofeedus]

Transformer Design and Supply still make the transformers for Bad Cat and Matchless AFAIK.
I ordered the 30W transformer set from them when I was building my clubman clone.
I don't recall any spec sheet for the choke they sent, but I bet you could call them and ask.
TDS Bill: 951-313-1648

[Stevem]

For the added 5 bucks or lessI would add the resistor also!

[turbofeedus]

For the added 5 bucks or lessI would add the resistor also!

I've only seen that resistor on old Traynors, is this something most companies aren't really concerned about? Do you put it on all your amps?

[didit]

Hello --

Pete Traynor (like Steve) had long years as working repair technician, and that experience reflects in his amplifier designs. Long & McQuade had (and still does) significant equipment rental business, and he was admired for efforts minimizing failures without impacting amp performance.

Best .. Ian

[norburybrook]

thanks Fellas.

So the resistor is literally from the 16 ohm tap on the switch to ground? how does that work when you're using the 16 ohm output into a speaker?


@joeboo88 thanks for the pic. I had a dumble type chassis lying around and a 50w OT and some EL34's and fancied something a little different and this seemed to fit the bill I'm interested to see /hear how it sounds. I was thinking of some kind of Marshall 2203 but thought this would be a little more interesting.

If I make it look nice I can always sell it if I don't like it. Mind you having a high gain amp in the studio will be a nice addition anyway.

thanks for the help.

p.s. as this is a hot amp would it be better to make this a 'Marshall' type tubes up rather than the Matchless/fender tubes down. My thinking is the heat will rise out of the way better tubes up.


M

[joeboo88]

I think tubes up would be best?
Although dccribbs1412 (Darin) a member here built one but in a head, tubes down.. his build is here

https://ampgarage.com/forum/viewtopic.php?t=15875

[PaulD]

So the resistor is literally from the 16 ohm tap on the switch to ground? how does that work when you're using the 16 ohm output into a speaker?

The resistor is in parallel with the speaker so you will have a total load of 15 ohms, the resistor being a much higher value than the speaker will only take a small amount of the output power in normal use (16/250 = 0.064)

[Phil_S]

I've never been able to understand a tubes down build. It makes sense to have the base on the bottom. Build a head and a cab. Maximum flexibility.

[turbofeedus]

I've never been able to understand a tubes down build. It makes sense to have the base on the bottom. Build a head and a cab. Maximum flexibility.

Yeah, after dealing with a few of these hanging chassis, I'd opt to even make a bigger combo and include a shelf for mounting the chassis tubes up.

[brewdude]

This is a small vertical 2x8 combo with tubes up.
Edit: I can’t figure out how to get the pic oriented properly.

[norburybrook]

I think tubes up would be best?
Although dccribbs1412 (Darin) a member here built one but in a head, tubes down.. his build is here

https://ampgarage.com/forum/viewtopic.php?t=15875

thanks for that link interesting.


Anyone care to give their thoughts on dropping the voltage of a fender PT 320-0-320 to nearer the 285-0-285 of the original? i.e. how to do it, and is it necessary?

I could always get a transformer made with the correct specs if needed from my usual supplier @inmadout in Italy, I'm worried that as it's running in class A the voltages need to be spot on.


M