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In Reply to: Ponderings on the PV10 vs. PV-12 posted by erik_squires@hotmail.com on July 19, 2006 at 18:48:37:
The PV-12 was built when CJ was using the polystyrene caps, and it made extensive use of them. CJ had them custom made, and one of their suppliers was Southern F-Dyne, who also builds for Krell and ML, among others. Their construction is impeccable, although my customs occasionally suffered from a lead breaking off.The PV-12 does not use a pre regulator for the filament supply. The circuit is identical to the PV-10.
The PV-12 drops the B+ in two stages, using the same circuit topology in series. It then uses the same circuit topology to supply B+ to the phono stages. IIRC, one set of VR's to provide for the front end tubes and the second for the back end.
Did you get the schematic and notes for modding the 10 that I emailed you? The simple addition of the cap to the filament lowers the filament ripple from 20 mA to less than 2 mA.
The diode isolation mod significantly increases stereo separation and detail. You can also use a larger cap to bypass the cathode resister for a nice gain in bass response.
Follow Ups:
Yes, I just got your mods today, I'll be taking a look at them this weekend.Sorry, I meant the B+ supply had a "preregulator" added to the regulator in the PV-10.
So does this mean that CJ gave up on the PS caps after the PV-12?
Does the "increase in bass" bring it up to flat, or does it give me a response hump?
I can't wait to try the filament cap mod. I measured the voltage across the 100 Ohm ground cap though, and didn't find a significan't voltage, you sure I can't use a smaller voltage cap there?
Thanks!
Erik
Basically the world's supply of polystyrene was halted in the first world countries, because environmentally, the production meant that some dioxin was present as a waste product. Since then I have heard that polystyrene plants have been established in China....
I blieve CJ bought up as much 'styrene material as they could, but some plants did not or would not sell the styrene unless CJ bought the finished goodes. There was a problem with the .1 uF bypass caps shorting out made in this period.
If everything is working properly, the filament ground is floating about 45 to 50 volts above true ground. CJ uses a voltage difvider from the b+ to get this polarizing voltage. I just feel safer using a higher voltage. Technically a 63 volt cap should be sufficient, but I buy a lot of surpls caps, and that's the vlaue I found cheaply.I consider the bass response increase closer to being flat. The increase in separation and detail is quite noticeable, however, and will up the performance to PV-11/12 levels if not more.
So, with the disapearance of ps, what does CJ use insteaed for bypass caps?Ahhh, filament ground, let me take another measurement, I was measuring across the 5W 100 Ohm resistor that's attached to the volume pot.
Speaking of spare caps, the thing about Julia Child's cooking that always got to me is that she always had all these "spare" parts lying around to throw in her cooking, so there was no way to just go out and buy what you needed and start cooking. You had to make a bunch of other meals to have the spare parts. :)
I'm a little leary of doing more to this preamp than adding the filament cap, and perhaps the 2 diodes (1/side). Suggestions on type?
The diagram on the top right of the PDF was a little hard to understand, could you tell me what I should be seeing?
Thank you again,
As Jeff pointed out, CJ has still stockpiles of PS caps. When they realize a worldwide commodity may disappear they move rather quickly. As a matter of fact I believe that's why the last production run of GE 6550's and 6CA7's disappeared so quickly in the mid to late '90's....
Sorry about the quality of the scan.
The picture in the right corner was supposed to be what you would see looking at the bottom of the PCB. It shows where to cut the traces and insert the diodes. I use a 1u4007, fast recovery type, and a a cheesy 5 to 10 uF electrolytic cap, making everything fit under the board.I've tried film caps, and they do sound a bit better, but the small electrolytics seem to work very well and have the advantage of fitting under the board.
You may want to try different coupling caps, especially if your unit runs Solens. I personally find them a bit slow and smeared. Try something like the Holland's or other premium caps.
Also if you'd like better bass, bypass the cathode with a larger cap. I use a 1.5 uF film cap for a nice increase in low frequency response and detail. There ought to be a small 'styrene cap there now, 150 pF or so.
I also make a bridge using AC caps (.1 uF) across each filament transformer output winding and from each leg to ground. I believe a lot of the spikes from the diodes are reflected back into the transformer, and this helps snub them. The result is a sound with more 'body' and presence.
Have fun,
Stu
PS. Oh yeah try putting real wire from the input jack to the selector switch. I like the kimber SF 23 oval wire.
...capacitor-quality polystyrene film IS available, and companies that made 'styrene caps before, still make 'styrene caps, and c-j still uses 'styrene caps in their products.Someone who should know but is NOT a c-j person told me that Reliable makes the c-jd 'styrene caps; I don't know one way or the other. I do know that c-j still uses lots of 'styrene caps in their 2nd-level (that is, below their best stuff such as the ACT2 and CT5) equipment.
If CJ only uses the PS bypass caps as 2nd tier equipment, what do they use in their first tier?
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