Forums - Plate chokes

crazy bill the eel killer

Ex Member

Plate chokes
11/04/05 at 02:20:34

Hello again guys,
I've been reading again( I should probably stop as everytime I read something I decide to include it in this project- translation, the cost keeps going up).

What started life as some component upgrades to my SE84CSEX has blossomed somewhat. Shortly after I started this project I realized that everything was going except the iron, so I decided to leave my beloved EX alone, and build a new one from scratch. I've had an enormous amount of invaluable help from members of this forum (especially Eddie - who doesn't he help ?), and I would be lost w/o it, I can't thank you guys enough, so its time for my last ( I hope ) question.

Since I've decided to include grid chokes, I figured why not replace the 47K plate resistor on the 6922 stage with a plate choke. Everything I've been able to find indicates to me that its a step up from using the ubiquitous plate resistor. So your thoughts on the idea would be much appreciated, along with the process and the math I need to size it properly.

As Mork would say " NANU NANU "

Bill
(sorry guys, I'm on my third vodka

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« Last Edit: 11/04/05 at 02:21:15 by Crazy Bill the Eel Killer »

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Obi-Vaughn Kentubi

Ex Member

Re: Plate chokes
Reply #1 - 11/04/05 at 03:43:49

Whoa! Do we have some money burning a hole in our pocket or what? Wink

If you go with the stock operating point of about 2.4mA plate current per triode section, a set of GOOD plate load chokes will cost you around $90/pr in M6, and a good deal more than that in Permalloy/M6 stripe. If you crank up the heat with another operating point, the cost will rise proportionately with the necessary size increase. Without actually doing the math, I'd guess around 80 Henrys should do it with the 6922's Rp of 2300 ohms.

Eddie

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crazy bill the eel killer

Ex Member

Re: Plate chokes
Reply #2 - 11/22/05 at 14:30:24

Thanks Eddie,

Sorry for taking so long to respond, but this got put on the back burner.

Are the 80 H and 2.5 ma ratings minimums and its OK to say get a nice 100H 10 or 20 ma version, or do I have to get close to those ratings. Also, after examining the spec sheets on all the plate chokes I could find out there, I find that some of them with close ratings have significantly different dcr's on the primary. How does that spec figure in to what I need to get. I'm kind of got it down to either an Electro-Print,Magnequest, or Lundahl unit, but I want to make sure I get the best one for this application. ???

Also, since I'm removing the 47K plate load resistor, do I have to modify the 10K psu dropping resistor. I figure(which is probably wrong, but who knows), that the 47K loads the plate of the 6922 and drops the B+ on the plate. Since the dcr of the plate choke is way different than 47K, I'm thinking I have to make an adjustment to the B+. Or, for some unknown to me reason, is it a straight swap of the 47k for the plate choke.

Thanks again Eddie for all your help. I'll be working on your cds this weekend.

Bill

PS. No I don't have money burning a hole in my pocket, ;) but I do have a nice Proceed BPA 2 doing nothing. It's going on Ebay soon.
My wife said I can do anything I want as long as I raise the cash from selling my old stuff. Did I step in S&&T with this woman or what. She told me the only way I'll get in trouble with this project is either spending OUR money, or making the SE84CSEX sound worse (which is one of the reasons I decided to build a whole new amp from scratch. I figured if I screwed it up I'll still have the Select). She absolutely loves the way everything sounds now. She can't understand how anyone could listen to cds (sorry Randy) or transistors after hearing tubes and vinyl.

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« Last Edit: 11/22/05 at 14:37:44 by Crazy Bill the Eel Killer »

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Obi-Vaughn Kentubi

Ex Member

Re: Plate chokes
Reply #3 - 11/22/05 at 14:45:42

Jack Elliano of Electra Print is the mayor of Transformerville. He'll help you out with your specific application if you'll give him a quick call. 100H would indeed probably be better, I simply put 80H out there as a minimum figure off the top of my head without actually doing the math.

You'll have to lower the supply voltage for sure. When you get the chokes, calculate the actual plate voltage to about 90V using the measured DCR and a current figure of 5 mA per triode section. Use a 680 ohm cathode resistor. Trust me on this one. Cheesy

Eddie

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« Last Edit: 11/22/05 at 17:05:47 by Eddie_Vaughn »

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Randy

Ex Member

Re: Plate chokes
Reply #4 - 11/22/05 at 15:51:43

[quote author=crazy bill the eel killer link=1131074434/0#2 date=1132669824] She can't understand how anyone could listen to cds (sorry Randy) or transistors after hearing tubes and vinyl. [/quote]

No offense taken, crazy bill .....

I agree that much of digital is dreck .....

However, not all digital is the same ..... just as all tubes and even SS are not all the same. My digital front end is "slightly above average" and I have had several visitors to my home who are vinyl freaks and observed that they could live quite nicely with my system ..... if they didn't have to make the financial investment that I have made.

When great attention to detail is given to the room and system setup, digital can sound very tasty indeed .....

Randy

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crazy bill the eel killer

Ex Member

Re: Plate chokes
Reply #5 - 11/23/05 at 12:20:06

Thanks Eddie,

For the record, I trust you on EVERYTHING.

At the risk of sounding stupid (its been a very long time since I've done any of this, and even then it was very simple stuff),how do I get the 90v @ 5ma to the plate. Do I have to measure what I have coming off the 10Kpsu dropping resistors, then figure what I need to add to the dcr of the choke to drop that to 90v, or do I measure before the 10ks and figure from that voltage to come down to 90v.

Since the adjustable bias feature was history anyway, I will gladly change the cathode bias to 680 ohms per side. Since I'm replacing a lot of resistors with the plate and grid chokes, I'm thinking of making both of the cathode bias resistors (the 680 and the 100 on the SV83) tants. That will give me only tants in the signal section of the amp. Is there any reason why tants would sound worse in this application than the Riken Ohms I've already purchased.

Thanks again for all your help.

Bill

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Obi-Vaughn Kentubi

Ex Member

Re: Plate chokes
Reply #6 - 11/23/05 at 15:14:55

FWIW, I'd use the Rikens for cathode resistors on the preamp tube, and a 5W Kiwame on the power tubes. But, tants will be OK too.

As for the power supply, I'd keep the stock configuration downstream of the 6.8K dropping resistor. In other words, just replace the plate load resistors with the chokes. Drop your voltage in one place by upping the value of the 6.8K resistor. Be sure to calculate the IR² heat rise and size the wattage rating accordingly.

Eddie

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crazy bill the eel killer

Ex Member

Re: Plate chokes
Reply #7 - 11/26/05 at 04:25:48

Hello Randy,

I couldn't agree more. I just quoted my wife to inject a little humor. While vinyl is my source of choice, I most definately enjoy my cds. While some send me running for the hills, the well recorded ones will bring a smile to my face and get my foot a tapping. Anyway, I've got vinyl that's so bad it will send me running out of the room.

After I finish this amp project, I'm going to get working on the digital front end. I'm not sure if I'm going to extensively mod my Marantz, or do something with one of the chip manufacturers evaluation boards. I know you've got a lot of experience with digital, so any advice or thoughts you might have would be much appreciated.

Thanks, Bill

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314159 Ex Member	Re: Plate chokes Reply #8 - 11/26/05 at 17:11:29 Bill, Let us know how your choke project turns out...if I get employed soon I may be thinking along the same lines. rt
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crazy bill the eel killer

Ex Member

Re: Plate chokes
Reply #9 - 12/14/05 at 01:18:54

Hello Eddie,

I purchased the 680 ohm Riken and 100 ohm 5 watt Kiwame per your suggestion, but your suggested values on the plate voltage and current have me confused. I bought Rozenbilt's and Jones's books, and reading them and your posts have been most helpful, and I'm actually starting to understand a LITTLE. I downloaded plate curves for the 6922, and your suggested 90v @ 5 ma looks like a grid bias of -2.4 volts. However, at 5ma the 680 ohm cathode bias resistor biases the grid to -3.4v. Since the numbers don't jive, I'm confused. Where did I go wrong?

Thanks, Bill

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