Choke for a 50W Plexi clone... woah the Hammond is 40H?!?!

[Hardtailed]

So yes I'm pretty set on Hammond iron for this project.
Mostly cause I can get it local for pretty cheap (the CDN$ took a dive over the last few months so buying canadian makes a huge difference).
The 1750N (OT for JMP 50W) and 290GX (PT for JCM 50W) are just perfect, price is good, and I've read nothing but good comments (someone here even liking them over Heyboer).

But then comes the choke, the only "Marshall" style choke in their new guitar amp line is the 193C which is rated at 40H!
Isn't that a lot?

I've read 5H at some places, 10H at others.
I don't want too much filtering as I like an amp that feels alive and dynamic, but I do like a very tight low-end.

So I'm trying to skim through their general line of chokes to find the best candidate, I've never used a choke before so I'm confused. Is 40H really too much? Does it really make a difference?
The 193C is also rated at 50mA... I know the choke is post power-amp, but it does have the screen and preamp current going through it.

What about voltage rating? They have anywhere from 300 to 800V offerings. Sure the amp is gonna be running close to 500VDC, but the choke being in serie, there won't be that much of a drop accross it? (or maybe that has nothing to do with it!)

Thanks for any help!

[black_labb]

the chokes voltage rating is for shorting to the frame (which is grounded). i'm pretty sure that the ratings are pretty conservative. i think the reason for such high inductance is the amp its designed for is a high gain amp, and dc filtering is very important to eliminate hum.

if your making your own amp, does it matter if the choke is "marshall style"? thats just there to fit as a direct replacement for a marshall amp. that doesnt mean that it is a bad choice for a choke by the way, it should be fine. i dont know wether it would make the amp less dynamic, someone might have to comment on that

[Hardtailed]

if your making your own amp, does it matter if the choke is "marshall style"? thats just there to fit as a direct replacement for a marshall amp. that doesnt mean that it is a bad choice for a choke by the way, it should be fine. i dont know wether it would make the amp less dynamic, someone might have to comment on that

Well, I guess it just seemed simple to just order whatever they have a for a Marshall 50W amp.

The have a huge selection of general purpose chokes though, but I was getting lost in their selection (which is not listed in any kind of logical way) and those that seemed to fit the bill seemed to be pretty big and heavy.

So I guess I need at least a 500V rating to be safe?

[daz]

First of all, where did you get that spec from? the 193c is what I have in a marshall style build, and it is 20H, not 40. Look it up at angela.com or tubesandmore.com. And it works great. My amp has a ton of punch with it and is not at all stiff. It''s dynamic and spongy. I wondered about even 20H being a lot, but both the matchless chieftain and badcat hotcat i think it is have 20H chokes. The only drag is they are pretty heavy and big for a d@mn choke !

[Enzo]

And remember, your filtration is the choke, the filter caps, the dropping resistors, and so on, not just... the choke. A little more choke than you want would be like having one of your caps a little larger than you want. it is part of a larger whole.

[Hardtailed]

First of all, where did you get that spec from? the 193c is what I have in a marshall style build, and it is 20H, not 40. Look it up at angela.com or tubesandmore.com. And it works great. My amp has a ton of punch with it and is not at all stiff. It''s dynamic and spongy. I wondered about even 20H being a lot, but both the matchless chieftain and badcat hotcat i think it is have 20H chokes. The only drag is they are pretty heavy and big for a d@mn choke !

Sorry, I mean 194C, the one that's part of their guitar amp line.
I'm just trying to understand why they made it a 40H since no ones seems to be using such big chokes.

I just notice that the generic line of chokes is ordered logically on AES (tubesandmore.com), much easier to browse!

If I want to go with 10H, I guess the best choice is the 193G with 10H, 150mA, 102ohms and 800VDC specs, but damn... 4.3lbs! I didn't except this... but whatever it takes

The 159P at 10H, 125 mA and 155 ohms and just 2.25lbs would be much nicer but I like a good safety margin and it's rated at 500VDC... Maybe I'm just pulling hairs here since even the filter caps aren't rated anymore than 500V usually.

[6267]

Quieter amps are more dynamic, usually, since you can hear the quiet instead of hum

[Bruce / Mission Amps]

You might find things have changed, but if you are trying to play the US dollar against the Canadian dollar, be careful when ordering directly from Hammond Manufacturing!
You are going to find out they will play a exchange rate game with you and probably not give you what you expect in terms of the listed $$ exchange rate.
In other words, in the past, they would charge the US dollar to the USA buyers and the CA dollar to the Canadians.
So a "$100.00" purchase cost me $100 (USD) and my friends in Canada paid $79 (USD) for the same thing.
After a few of those tricks, I stopped buying directly from them.

[Hardtailed]

I probably won't be buying directly, I have a local Hammond distributor.
I'm basing myself on a1parts.com to figure out the prices though.

For example, on a1parts.com, the 1750N OT is 75.95$ CDN
If I go on tubesandmore.com, it's 78.45$US
The exchange rate is currently 0.7943$US for 1$CDN, so that's 98.76$CDN + shipping, for the same part. This is why I want to buy local

As for chokes, the 159P is 25.42$CDN, while the 193G is 52.68$, so hopefully the 159P (10H, 125mA, 500VDC) is good for the job.

Does the serie resistance of the choke makes a big difference?
For example, the 159P is 155 ohms while the 193G is 105 ohms.

Thanks to everyone who chimed in!

[Bruce / Mission Amps]

The main thing to keep in mind is that, (disregarding the minimal amount of current used by preamp tubes), EL34 amps draw a lot of screen current while 6L6 amps don't pull as much.
That screen current is being drawn through the choke..... as is the preamp tube's idling current.
What this means is, what ever choke used, needs to have a current rating high enough that at a specific screen current draw, the inductance is still 5Hy to 10Hy. The actual measured inductance in most chokes varies by the amount of current in the winding.
As an example, I don't think a small 50ma-90ma 3Hy-5Hy choke, found in lots of push pull 6L6 amps will be any good in an EL34 amp.
At idle or at rest, the small choke would work as advertised but not when playing loudly or rocking out.

I'd used something that was at least 5Hy to 10Hy and rated at 150ma or so.
A 159Q Hammond choke would probably work OK though... and don't worry too much about the voltage rating as that is more about the voltage drop across the windings.... it is actually very small in the choke when measured.
Yes, a shorted circuit down stream could drop the entire B+ to ground but I've used lots and lots of the smaller, 400v chokes, such as the 158Q in amps running 460vdc to 480vdc. To date: ZERO choke failures.

The actual DC resistance of the choke:
the whole idea of a choke in the B+ rail is to have very low DC resistance and very high inductance with a usable current rating.
In your EL34 amp, a low DC resistance means you should have separate screen resistors on the tube sockets.
Mostly to insure the actual screen voltage (nor current) is too high with respect to the plate voltage... especially when the amp is rockin'.
That is why you will see EL34 amps with 1000 ohm screen resistors..rather then none or the small 470 ohm screen resistors seen in many 6L6 or (even 6V6) amps.
However, due to the larger screen current draw seen in EL34 amps, those amps will need 5 watt resistors instead of 1 watt ones found in the 6L6 or 6V6 amps.

[mr.jetski]

hi all,
from what i learned and understand of it, the choke voltage was determined by what you HT is. The ohms number was the difference between HT on the OT (and by extension the tube plates) and the control grids. the henries number is the filtering ability. did i miss something?

[Edgar Sterling]

Choke voltage rating

Bruce at Mission Amps said:

"I'd used something that was at least 5Hy to 10Hy and rated at 150ma or so.
A 159Q Hammond choke would probably work OK though... and don't worry too much about the voltage rating as that is more about the voltage drop across the windings.... it is actually very small in the choke when measured.
Yes, a shorted circuit down stream could drop the entire B+ to ground but I've used lots and lots of the smaller, 400v chokes, such as the 158Q in amps running 460vdc to 480vdc. To date: ZERO choke failures."

Does this statement about the voltage rating hold true for both a choke input supply as well as capacitor-choke-capacitor pi filter type? I just got this 158q and I'm wondering if I can use it in a choke input design; I've got a hotter than average PT that is putting out 450V from pin 8 of NOS 5y3. From what I've read this configuration could drop the supply voltage a lot.
Thanks,
E Sterling