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Old 9th January 2013, 10:13 PM   #351
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Changing the subject a bit, have any of you guys used anything like dampeners around the bottle of the 4P1L? It's about 28mm diameter. A friend suggested this very cheap and useful box of O-rings. They include 25 x 3.5, 26.5 x 3.5, 28 x 3.5. For a preamp this looks useful:

419 PIECE RIC RUBBER O RING SEALS SET PLUMBING TAP WASHER ORING PLUMBERS | eBay

I've been using teflon plumbers tape. I'll see if I can upload a picture.
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Old 9th January 2013, 10:24 PM   #352
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Teflon plumber's tape around the 4P1Ls in my preamp.
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File Type: jpg 4P1L.jpg (919.0 KB, 396 views)
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Old 9th January 2013, 11:35 PM   #353
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I bought a 10 pack of 3mm x 26mm viton 75 high temp o rings, nice tight fit, didn't make much difference, they still sing along!

enzo
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Old 10th January 2013, 09:34 AM   #354
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I'm looking for a DHT headphone amp for my Sennheiser HD600, I saw this schematic regal posted in other thread of moglia.

Click the image to open in full size.

I have several questions:

-Can I use only one Salas SSHV2 for the two anodes?
-If yes how much current have to set plus de 20mA required for the reg?
-Value of interestage capacitor?
-Value of resistor for bias filament & Rod Coleman heaters reg?
-The OPT for my Senns must be 5K:300ohms or lower?
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Old 10th January 2013, 10:07 AM   #355
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hi Felipe,

It's possible to use one shunt-regulator for power and driver stages. But if each stage draws 30mA each the standing-current will be 80mA or more at 150-250V (you must choose your B+ value in this range - draw some load lines for the output transformer you plan to use. Ale has some triode curves posted here somewhere, I think). Please check that your regulator can support this high power level (depends on power transistors, and size of heatsink).

It will work better if you use 1 shunt regulator for drivers, 1 for power stage, I think.

for e.g.: 200V B+, the filament-bias resistor is chosen like this:

- bias required at 200V: 15V approx for 30mA (Anode dissipation <6W - against max. of 7,5W).

- filament current 500-650mA (adjustable to suit 1,2V connexion)
- bias resistor = 15V/If = 24 to 33R
- resistor power dissipation: 7,5 to 10W. Use 3 or 4 parallel 100R 10W wirewound, eg Welwyn W23 or W24.

At 150V B+ the bias is about 10V so you can use about 20 ohms with 15W handling.
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Old 10th January 2013, 10:59 AM   #356
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Thanks Rod, do you know if can handle high Z headphones? insterstage cap value 100nF or 47nF? do you kow secondary value of OPT?
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Old 10th January 2013, 11:14 AM   #357
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Hi Felipe,

Grid resistor of 500K is specified, BUT the tubes are old and you are planning to use fixed bias, at least for the output stage. Maybe use 330K for the driver, 220K for the output stage (Anatoliy will have more experience of the actual 1st-grid leakage value).

In this case, 100n for the driver input coupling cap, 150nF for the output stage cap.

As for high Z headphones - should be OK, but the load line of the transformer-load must be plotted, to make a proper check.
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Old 10th January 2013, 12:14 PM   #358
regal is offline regal  United States
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Quote:
Originally Posted by merlin el mago View Post
I'm looking for a DHT headphone amp for my Sennheiser HD600, I saw this schematic regal posted in other thread of moglia.

Click the image to open in full size.

I have several questions:

-Can I use only one Salas SSHV2 for the two anodes?
-If yes how much current have to set plus de 20mA required for the reg?
-Value of interestage capacitor?
-Value of resistor for bias filament & Rod Coleman heaters reg?
-The OPT for my Senns must be 5K:300ohms or lower?
The intent was that the SSHV would supply the output tube only because the input tube has a DN2450 casode, prefiltering is CLC. Otherwie your case would be a big ugly heatsink.

The coupling cap is .5uf (copper foil PIO), I didn't draw the grid leak resistors, should be about 100k. Also would recommend the filament bias on both tubes.

But if you are as interested in hearing how this sounds as I am we both need to find a good output transformer. One that is designed from the ground up for headphones not speakers, this is what has been holding me back on the project. A good headphone transformer is more than just winding a long secondary on a speaker transformer.

We want to take advantage of the lower stepdown ratio but at the same time not end up with a ridiculous 12 ohms DCR in the secondary. Parafeed permalloy may be the best answer, this is why the project is at a standstill there are practically no output transformer designers left who are willing to work with an individual for a novel OPT design. For senns be very careful you don't end up with a crazy 200 ohm DCR secondary. If you have any help on that end let me know.

Last edited by regal; 10th January 2013 at 12:17 PM.
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Old 10th January 2013, 12:18 PM   #359
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I know one person in Spain how makes hand made grain orientated, can't be enough? what about Lundhal LL1689 http://www.lundahl.se/pdf/1689.pdf, can be wired 9:1 or 18:1?

Last edited by merlin el mago; 10th January 2013 at 12:22 PM.
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Old 10th January 2013, 12:35 PM   #360
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Sowter still offer custom OTs to any who fill out the form:

SOWTER TUBE VALVE OUTPUT TRANSFORMERS

Not exactly cheap, but no charge for the design work, so you can really get something optimised. They have a huge range of Prosound mixing desk, line & headphone trafos, too, so Brian will know just how to implement your requirements.
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