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In Reply to: RE: Too bad Panhead posted by 1973shovel on March 10, 2015 at 04:19:00
He may not be comfortable posting. If you would like to find out more, I could possibly arrange to get you his phone number, and you two guys can have a real time back-and-forth discussion ! I know he likes to use the phone, and is VERY enthusiastic about what he is hearing, experimenting with, when he communicates to me.
Jeff Medwin
Follow Ups:
It was directed at Panheadchopper's Dynaco MK-III post, because they're amps I happen to own. But the question could be applied to almost any amp where the resistance value of the choke is reduced. (Link to my question below).
I suppose you could broker Panheadchopper's phone number for me, but I suspect that given his moniker, we'd likely do a lot more talking about Shovelheads and Panheads (old Harleys, for those not aware of it) than we would amps.
In the meantime, would you care to respond to my question? When you reduce the DCR of a choke, do you compensate by adding resistance to other sections of a circuit, to bring voltages within operating parameters?
Thanks.
The Dyna MK2 used a 50ohm resistor IIRC. So depending on the DCR of the C354 choke used in the MK3, it's probably close enough. And in those days people didn't worry that much about running tubes hot. Most good old American tubes could easily take it and replacements were cheap and plentiful.P.S. I see below that Mr. Lowmu has indicated the stock C354 is 55 ohms. So there you go, it's a perfect DCR for that circuit, they probably wound to that DCR for that reason. But yes, if you lower the DCR of a replacement choke, you have to be careful with too much B+. And the Dyna MK2&3 ran high anyway plus the line voltage in the early 1960s was more likely to be 115v. One solution is a Variac (expensive) or buck transformer (cheap) on the primary.
Edits: 03/11/15
The point I was attempting to make, or more accurately, what I was attempting to learn was if any subjective sonic improvements were simply due to the increased voltage caused by the substitution of a low DCR choke.
A bucking transformer, as well as NTC limiters are a wise choice for these old amps.
Thanks.
Yes, swapping out legacy chokes with low DCR parts can certainly make sonic improvements. As you will be pushing the B+ up a significant amount, most amps will sound better when operating at higher B+.
But the rub is you are now possibly stressing tubes and other components. And especially the 50 year old components that can be fragile.
My advice is to measure the B+ and make sure you aren't stressing anything with your new low DCR chokes.
Which was my point.
So I should be able to get the same sonic benefit by increasing B+ and leaving the choke alone.
I would say yes. Because replacing say a 2h 50ohm DCR choke with a 0.35uh 5 ohm choke would elevate the B+. However you have now lost a significant amount of ripple filtering with the millihenry sized choke.
So if more B+ is your goal, reducing the choke DCR is only a good option if you can maintain the same or close henry value.
And again I must stress that bumping up the B+ to get a more dynamic or aggressive sounding amp is not a good practice. Most commercial amps were designed at the optimum operating points. Some even beyond that such as Dynaco because tubes were cheap in those days. And remember that line voltage in the 1950/60s was 110-115v. Today we have 120-125v.
You really need to carefully analyse the circuit before raising the B+.
Hi,
I will ask Panhead if he will take a call, and get back to you ASAP.
I always figured your moniker meant vintage Harley !!
You ask: "When you reduce the DCR of a choke, do you compensate by adding resistance to other sections of a circuit, to bring voltages within operating parameters?"
Well, you can, if necessary, add resistances to the power supply going to the front end stages, that is usually NOT a problem to do, if needed.
But, adding to the Finals is a whole different thing. We wanna have as LOW a series resistances as we can get , to the Finals !!!.
Lets talk MK 3s. Lets say, the stock choke is 55 Ohms, and we, as ONE example, replace it with two small 7.8 Ohm chokes - totaling 15.6 Ohms. So, the stock single L/C filter is replaced with / becomes L1/C1/L2/C2. 55 Ohms minus 14.6 Ohms is a reduction of 39.4 Ohms in series to the Finals.
Lets say, the whole MK.3 pulls 140 mA., what is the voltage increase with the lowered series choke resistances ?
That is Ohms Law, 0.014 A. times 39.4 Ohms, equals 5.15 VDC increase of the B+. Lets say the B+ was 425 VDC, well, that is only a 1.3 % increase in B+. However, the MK. 3 PLAYs a whole lot different, according to what Panhead tells me. AS I recall, Mark used 2 HY at 9.5 Ohms, a single choke replaced.
I HOPE I have answered your Question OK. Will ask Mark if you two motorcycle enthusiasts can speak !!! Later !!
Jeff
I'm still curious how much of the sonic improvement would be due to the increased voltage, as Jim McShane speculated about different brands of rectifiers.
I suppose the only way I'll know is to try it for myself. Xaudiomanx often posts that he preferred the sound of his Dynaco amps with the choke removed, with a resistor substituted. I never got around to trying that either, mostly because it defied my logic of what should be the better power supply configuration.
Probably not the best methodology on my part.
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