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Repairing Hi-End Preamplifier
Repairing Hi-End Preamplifier
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Old 16th April 2018, 06:04 PM   #111
Pars is offline Pars  United States
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You could see if they would either sell small quantities direct, or request samples...
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Old 17th April 2018, 03:09 AM   #112
Bigun is offline Bigun  Canada
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Repairing Hi-End Preamplifier
One option is to repair to blueprint, put it in a display case as a valuable unit. Then DIY a clone with the suggested reliability improvements and use it as your daily driver. You would have an original to compare it with and maybe a whole bunch of folk here would join in and make a clone too.
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Old 17th April 2018, 10:21 AM   #113
jahsavage is offline jahsavage  United Kingdom
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Quote:
Originally Posted by Pars View Post
You could see if they would either sell small quantities direct, or request samples...
The CCLH100 diodes which I think you refer to had a link time of 14 weeks which also put me off!

CCLH100 TR Central Semiconductor | Mouser United Kingdom
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Old 17th April 2018, 04:29 PM   #114
RJM1 is offline RJM1  United States
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Back in the 90's I was repairing a unit for someone and the lead time on the diode that it needed was 6 months from all suppliers. I contacted the company directly and told them that I needed to purchase this diode. Their reply was " I'm sorry, but they will not be available for 6 months, but I can send you some free samples..."
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Old 18th April 2018, 10:47 AM   #115
jvhb is offline jvhb  Europe
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Repairing Hi-End Preamplifier
Quote:
Originally Posted by analog_sa View Post
You would be surprised how many audiophiles own Philips screwdrivers. And are not afraid to use them
- And don't realize that the screws most often are actually JIS and not Philips type..
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Old 18th April 2018, 11:15 AM   #116
Demonkleaner is offline Demonkleaner  United States
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In amateur radio it's sometime known as the "golden screwdriver".......
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Old 18th April 2018, 05:07 PM   #117
hpeter is offline hpeter  Slovakia
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Quote:
Originally Posted by jahsavage View Post
So I ordered the following 100v CCDs from Mouser
954-E-562 x8, 5.6ma
954-E-352 x2 3.5mA
954-E-452 x4 4.5mA
954-E-272 x2 2.7mA

I intend to use 2x5.6mA and one 4,5mA in parallel to give 15.7.mA for PS regulation and a 5.6mA and 4.5mA to give 10mA to supply the anode, that will leave 5.7 for the zener branch. Since postage was free over 33 I added a few others just in case more current or different values are required,

The CCLH100 series of constant current diodes looked idea until I realised I had to order 2,500 pound worth
this schema is nothing special there, just a bunch of ccs diodes.
which does NOT give much high impedance to triode. and next stage will lower the loadline further.
in general, ccs diodes impedance is waay below what gyrator can achieve. and you will parallel few of them.

basic plate resistor is slightly worse in this respect.

id go with fet gyrator, which gives ~5 megohms for driver tube (small thd), and output resistance is much lower, not affecting the tube stage.
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Old 20th April 2018, 02:11 PM   #118
jahsavage is offline jahsavage  United Kingdom
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The parts arrived yesterday and fortunately they look identical to those being replaced. Before rushing ahead I decided to have a rethink. My tests showed the zeners used did not require much current to breakdown. I found these data sheets online 1N4125 pdf, 1N4125 description, 1N4125 datasheets, 1N4125 view ::: ALLDATASHEET ::: , which required only 1mA to be in the middle of their operating range.

This fitted in nicely with the original design that used only two CCD's, so I used two 5.6mA in the power section of the circuit and a 5.6 and 4.5 in the anode leaving 1.1mA for the zeners. This seemed like a risk worth taking since over current may damage the zeners.

So I rolled the dice and believe it or not it worked first time. First impressions are that it sounds as before but I'll shall reassess after some serious listening.

Again, thanks to the forum for their help - .time for a beer or two!

After comparing with another preamp the sound is very 3d and flowery but a bit distant. SO I suspect the bias spot is not quite on.

I measured the anode voltage and its 99v and stable once the power supply has warmed up. Looking at the bias curves I'm wondering if I need at least another 5mA on the anode?
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Old 20th April 2018, 06:32 PM   #119
anatech is offline anatech  Canada
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Repairing Hi-End Preamplifier

Okay, you're speaking a different language and I haven't any way to translate that.

Be happy.

-Chris
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Old 20th April 2018, 06:44 PM   #120
Bigun is offline Bigun  Canada
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Repairing Hi-End Preamplifier
Quote:
Originally Posted by jahsavage View Post
I'm wondering if I need at least another 5mA on the anode?
just one tiny tweak eh?

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