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In Reply to: Re: End Of Zen schematic posted by Anand on October 30, 2001 at 07:18:25:
Seems like that's another nice alternative to the 125E. Kinda nice since 5K parafeed transformer prices seem to skyrocket after that.My original intent was to build up about 10 of these amps and sell them to folks (hence the careful selection of parts to meet a budget). Since metalworking is not a strong point of mine and aesthetics wouldn't be great for what I'm able to do, I decided not to do it. I did find a nice chassis manufacturer but the cost of the chassis would double the parts costs! Maybe I'll just buy one chassis and redo the amp that I did build.
Tom §.
Follow Ups:
I'm actually going to get IAG out in Killeen, TX to build my chassis. They have those nice polished aluminum ones that look nickel plated but are not. Reasonable prices too. But, nothing like doing your own on a hammond.Good thing your schematic is so simple to follow. I was also thinking of the Handmade H3008 plate choke, but its specs look very different from what you have specified so I guess it'll have to be the Magnequest BCP-15.
Anand.
Hey Anand,Let me begin by saying I am no guru but...
I think the H3008 may be more suitable here.I believe the Hammond was chosen by Tom as the choke because it was a budget part that could do the job at hand while being easily obtainable, budget being the operative word here. Its a power supply choke and not a plate choke so there are some compromises (as always)in its use as a plate choke. Tom can straighten me out here.The rule of thumb for the choke I know of is preferably ~20H per 1K primary Z so if you are using a opt with a 5K primary you want ~100H. Thats not to say that 15H or 30H will not work, the extra inductance is supposed to work better.
There is another rule of thumb I have read where the opt inductance should be ~4X the choke inductance, so... if you have a 100H choke you want an opt ~400H (thats a lot!!).
Thats part of the reasoning behind the fancy materials in the opt's, higher inductance.
Now, having said all this I have seen more than one design where the choke is ~80H and the opt ~20H, which is the opposite and of course it works.
I breadboarded (new word!) a "parazen clone" 6n1p - Triode wired el84 with a PP opt as choke and 125e as opt and it worked quite well.
I guess with all the rules it still all comes down to trying it and listening to see how it works, just like what Tom did.AB
> > . Its a power supply choke and not a plate choke so there are some compromises (as always)in its use as a plate choke. Tom can straighten me out here. < <One thing paul joppa has mentioned about plate chokes is the resonance point . Not that this should be the primary factor but another thing to consider when making the purchase decision. I've measured power supply chokes with resonances at 6khz and a couple at 4.5khz. One plate choke I had measured had a resonance around 3khz. IMO, it depends more on the stray capacitance of the choke rather than what the dealer brands it as (plate or power supply). The stray capacitance is all over the board for different makes of chokes and labelling chokes as "plate" or "power supply" doesn't make much difference. In all honesty I haven't measured the 157G's inductance curve and I've been using the BCP-15 for a few months now. I did use a 156G for the plate choke for quite awhile and the sound was about 90% of the quality of the BCP-15 in this circuit.
> > The rule of thumb for the choke I know of is preferably ~20H per 1K primary Z < <
I made my choke value decision based on the rp of the tube. A 30H choke would put the -1dB point at 20hz when used to load a 12B4. 60H would only give you -.5 to -.6 at 20hz. You have to realize that the plate choke inductance is in parallel with the tranny primary inductance when referenced to the tube. Most non air-gapped transformers provide craploads of inductance leaving the deciding factor on the plate choke. I think I measured around 560H on an all permalloy TFA-2004 at 20hz. I imagine the 125E is no slouch either.
Just keep in mind that even with a 9H choke in, this circuit still produced great sound. Going to higher choke values only optimized circuit performance rather that dramatically transforming the circuit sound. It still works and it still produces similar sound with "budget" parts. The parts were chosen for cost/performance ratio. When you plan for production, there's not much sense in spending 700% more for only a 5-10% increase. The customers can spend that money if they personally feel it's worth it. I fully encourage using better performing parts but I also encourage keeping it within reason and personal budget. You can build another project with the cost difference in a single part! There's a lot of fun and satisfaction in building a great performing amp for under $200. I could have easily spent $800 on this project by just using fancier iron. The question is: would it have been worth it?
Tom §.
Thanks Tom. I see your point. Thanks for the "resonant Point" link.
I think the last sentence of my former post sums it up..."I guess with all the rules it still all comes down to trying it and listening to see how it works, just like what Tom did."
AB
Actually, it seems the H3007 (and H3008) would make a decent choke in this circuit because of its ratings and cost. It'd be nice to have a frequency vs. inductance plot of these 2 chokes for comparison.Tom §.
here's another new arrival on the plate choke scene - the one electron units, for $60., can do 48H at 75 ma and have the interesting series/parallel options.
I'll see if Anthony Cirella can post a frequency vs. inductance plot of these two chokes on his site or this site.Anand.
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