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Old 17th August 2003, 10:40 PM   #1
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Default Help with plate chokes

I tried to use some Hammond 150H plate chokes in place of the 10K plate resistors. The Hammonds are 3700ohms in resistance and 8mA.
When I fired up the line amp the 5687 was microphonic and ringing. I then returned to the 10K plate resistors and everything was fine once again.
I will attach the schematic. Other modifications to the circuit include the usage of a VR150 and VR90 regulator tubes for a final B+ before the plate resistors of 240volts.


Joe
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Old 17th August 2003, 11:54 PM   #2
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Hi,

Quote:
When I fired up the line amp the 5687 was microphonic and ringing.
Joe, I hate to say to people "I told you so".

You know what I mean, don't you?

Cheers,
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Old 18th August 2003, 01:11 AM   #3
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Frank
Someone had posted before that these chokes were the way to go and they were only $8.00 a pop. I guess that all that glitters isn't gold. Is it possible that they need to be used so that the correct load is put on the plates?
Could you explain the ringing and why it happened? I was under the assumption that the choke would present a load the plate would like better than the resistor.
Could you suggest a choke that would work or am I barking up the wrong tree?

Joe
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Old 18th August 2003, 01:26 AM   #4
316a is offline 316a  England
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Default $8 Choke

Quote:
Originally posted by burnedfingers
Frank
Someone had posted before that these chokes were the way to go and they were only $8.00 a pop. I guess that all that glitters isn't gold. Is it possible that they need to be used so that the correct load is put on the plates?
Could you explain the ringing and why it happened? I was under the assumption that the choke would present a load the plate would like better than the resistor.
Could you suggest a choke that would work or am I barking up the wrong tree?

Joe
Hi Joe ,
You get what you pay for ! Why not try a current source or an SRPP/mu stage in place of the resistor ? May even be cheaper than the chokes to implement

316a
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Old 18th August 2003, 01:46 AM   #5
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Hi,

Quote:
I guess that all that glitters isn't gold.
You experienced it so you should know by now...

If you read my mail carefully you should notice my warning in that the chokes are non-linear resistances to the plate...

The chokes you put in there are PS chokes, NOT meant for this service as you found out the hard way.

The ringing can come from a number of factors, in this case you have created a resonant tank that's hard to tame.

As I said before, those chokes weren't meant for this service.

Quote:
Could you suggest a choke that would work or am I barking up the wrong tree?
No, you're not. Just make sure you understand what it is you're doing...don't expect to learn all this in a few months.
Take your time and try to understand that there's no need to jump a learning process.

Joe, if we're going to be just a bit smart, instead of use a plate choke, why not use a SE xformer and be done with it?

Cheers,
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Old 18th August 2003, 07:10 AM   #6
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I've had good results with 5687 and Lundahl LL1668. The ringing you hear is Joel's scream to always use the cheapest.
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Old 18th August 2003, 10:52 AM   #7
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analog_sa and Frank

Would you say that the LL1668 would work for this line amp or is there something better out there? I have found them listed for $72.00 ea at K&K Audio in NC.

The ringing was like having a mic input turned up all the way and being a foot away from the speaker.

I do believe I have proved the $8.00 choke doesn't work.

Joe
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Old 18th August 2003, 11:19 AM   #8
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Joe

I can't quite see what is your PS voltage but you certainly realise that with a plate choke the PS should be lowered. If you simply replace the plate resistor with a choke your plate voltage will certainly raise. As much as i don't advocate the use of PS chokes as plate loads there is no way i can guarantee that the strange sounds you hear are entirely due to the choke. In any case you would hardly regret buying the Lundahls - they make great loads in line and also driver stages. I keep having doubts if i really like the sound of interstage transformers in driver configurations, but the chokes categorically sound good. They may not provide the smoothest possible tonal balance but the improvements in dynamics and rhythm over resistors are well worth the price. Can you do better than Lundahl? No doubt, but the prices of the better stuff are obscene.


cheers
peter
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Old 18th August 2003, 11:33 AM   #9
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Hi,

An SE OPT for the 5687 would work as well and would do away with the coupling cap.

This may not be the cheapest solution, maybe not even the best sounding.

As Peter suggested the Lundahl choke should be fine but the PSU voltage should be lowered as the voltage drop of the choke is much smaller than the plate resistor.
There is an advantage here as you could then use a tubed regulator to drop the voltage.

An example:

Cheers,
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Old 18th August 2003, 12:06 PM   #10
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Hey-Hey!!!,
WIth this schematic that Frank has drawn, you should be able to get away with B+ from 150( a single VR150 ) to 220( maybe three VR75). If yo put in two VR sockets you can do a bit of mix an match to get just the op point you want. I did jsut this for my linestage and now have three 0C3 for a bit over 310 volts.
regards,
Douglas
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