Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: hesamadman on December 23, 2014, 02:31:46 pm
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Im working on the power amp of my AC30 build. I still need to acquire a choke. I spent a lot on transformers already Im trying to find cheapest option I can. AC30 chokes are in the 40 range. I know some jcm800 chokes are about 15-17 dollars. Do I need to be real specific with these anyway?
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For a 4 x EL84 based amp with a CLC filter supplying the screen and pre-amp nodes only, you want something between 3-10H, with a minimum DC rating in the vicinity of 100mA
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If it were my amp, I'd wait another paycheck or 2 (or for a tax refund) and buy a 15-20H choke, towards the top of end of value listed on the original AC-30 schematic. These amps don't have a whole lot of filtering to their power supply, and it's worthwhile in my mind to get the right part, rather than the "Right Now" part.
:icon_biggrin:
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The one AC30 schematic I looked at indicated it had a 20 H (Henrie) choke. I would size it to have the same ma rating or larger rating as your PT.
I looked at the Hammond site, found they provide 5 and 30 H chokes for AC30 reissues.
Good luck with your project.
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I would size it to have the same ma rating or larger rating as your PT.
Why would you say that?
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I would size it to have the same ma rating or larger rating as your PT. :w2:
Why would you say that?
you had to stir... :laugh:
DRGZwhatever.. the stock AC30 part is 20H @ 100mA. one of the replacement PT is rated at 270mA (classictone). DO YOU KNOW HOW LARGE A 300mA 20H CHOKE IS? or do you just troll? couldn't you at least research before guessing and posting misinformation?
--pete
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I would use as big a choke as I could fit in the space I had available for a AC30
The power supply needs all the help it can get
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DO YOU KNOW HOW LARGE A 300mA 20H CHOKE IS? or do you just troll? couldn't you at least research before guessing and posting misinformation?
I've got a few 250-500mA chokes (IIRC, 5-10H for the higher current rating, 20H for the lower current rating), robbed off an old regulated tube power supply which was choke-input.
The 500mA choke is bigger than most 100w output transformers. I never weighed it, but I'd guess over 10lbs, easy. The 250mA choke is also bigger than most 50-60w output transformers. Safe guess would be every bit as big as the power transformers that fed them.
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I would size it to have the same ma rating or larger rating as your PT.
Why would you say that?
I am curious, did you undersize the choke on the sunn spectro spectre schematic published several years ago? (typo)
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I would size it to have the same ma rating or larger rating as your PT. :w2:
Why would you say that?
you had to stir... :laugh:
DRGZwhatever.. the stock AC30 part is 20H @ 100mA. one of the replacement PT is rated at 270mA (classictone). DO YOU KNOW HOW LARGE A 300mA 20H CHOKE IS? or do you just troll? couldn't you at least research before guessing and posting misinformation?
--pete
Pete,
I know from your postings you have a strong VOX background, so you know there are several AC30 variants, including at least one where the choke was eliminated. Hopefully Hesmadman, will tell us, which variant of the AC30's he is building.
I see your point regarding the 100 ma choke with a 270 ma PT. (I couldn't find PT specs on Mercury Magnetics website.) The 100ma choke is partially filtering the PI and preamp blocks on the chassis.
As you are likely aware, many of the early fenders used chokes as part of a PI filtering system, on the entire B rail.
I would expect the choke to weigh 10 to 18 lbs.
The following is short list of schematics which use a PI filter on the full B rail. Fender 5f4; 1971 sunn sceptre (Diagram by Steve Luckey); gretsch model g6155/g6156 (field coil); pro amp 5e5 and 5e5a; Fenders 5d6 and 5d6a; princeton 5e2 and 5f2; The lowly 5e1.
With the price of iron and better caps, I will venture a guess that later versions of the amps, either lost the full rail pi filters, or the choke was replaced with resistors. (Too many MBAs). Then again higher capacity caps, also changed the playing field.
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I am curious, did you undersize the choke on the sunn spectro schematic published several years ago?
Never heard of sunn spectro. What does that have to do with anything in this thread?
I had a typo; change spectro to spectre.
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Steve,
Please find attached a copy of the Sunn Spectre 1971 schematic, that is attributed to you.
To answer your "why" question, I am looking for insight in sizing a choke. The generic name of this thread, to suggests an expansion beyond the specific choke chosen for the AC30 would be valuable information.
The spectre has a pi filter (CLC), smoothing the B rail voltage. I am just asking how you sized or would size the indicated choke, as there is no apparent data on the choke. The nature of your response suggests that I am not even in the ballpark, much less in left field. I can find the info on the PT from the information provided.
From other threads on this forum, I have developed an understanding that you are familiar with the various AC30 schematics, which differ from the specture.
And for others, the filtering scheme on the Sunn Spectre is different that the AC30, as the AC30's which use chokes, use chokes to smooth the B rail after the power is taken off for the center tap of the O/T. In the AC30 the choke is sized about 1/3 of the ma rating the P/T, (Which makes sense).
Looking forward to your response.
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This is the hoffman AC30. What have some of you guys who have built this used?
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I just ended up getting a classic tone. 20h, 10ma
The hammond seemed like an odd size. It was only 5h. And the other ac 30 choke they had was 30h. I took HBPs advice on the 15-20h choke.
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I just ended up getting a classic tone. 20h, 10ma
The hammond seemed like an odd size. It was only 5h. And the other ac 30 choke they had was 30h. I took HBPs advice on the 15-20h choke.
a wise choice if it's 100mA and not 10mA! ;-)
--pete
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I just ended up getting a classic tone. 20h, 10ma
The hammond seemed like an odd size. It was only 5h. And the other ac 30 choke they had was 30h. I took HBPs advice on the 15-20h choke.
The 30H choke would have been good too. Mo' filtering (though people debate whether more/less filtering on an AC-30 is a good thing). Bottom-line, you'll be fine.
a wise choice if it's 100mA and not 10mA! ;-)
Yep, ClassicTone's part is 20H, 100mA.
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I really like an el84 driven amp. As this will be my first el84 build, I will try the 30h choke on the next go around.