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DigitalJunkie DigitalJunkie is offline

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  • Last Activity: 28th August 2014 09:52 AM
  • Join Date: 30th April 2003

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Posted 2nd April 2012 at 08:37 PM by DigitalJunkie Comments 3
Posted in Uncategorized
So,one of the monitors I use decided to die yesterday,it came back from standby,but had rainbow lines all over the screen..Something in the TFT panel itself,COF or something.Gaw.

Anyways,it had built in sound,using a TDA7496L chip for the amp..I got to looking at it,and decided to pull it off the PCB and build a (headphone)amp with it.

It's basically the schematic on the datasheet,with slightly larger input and output caps,and it's all powered by a 3-cell Li-ion pack for a Vcc of about 11-12V.

Here's the datasheet.
http://www.st.com/internet/com/TECHN...CD00001216.pdf

It doesn't sound tooo bad,really. It's not the best thing ever,but for a couple hours of tinkering with junk that was on the bench, I'm pleased.
It's got more than enough power for 'phones,some care needs to be taken to prevent any accidents.

So yea,yesterday was more or less; Troubleshoot monitor,discover...

Posted 29th January 2012 at 07:52 PM by DigitalJunkie Comments 5
Posted in Uncategorized
So,I've been pondering this for a while,and I'm going to finally build it.

Basic idea- Fairly simple Push-Pull amplifier,that will deliver ~50Wpc,Using common/available tubes.
I decided to go with the 'usual' octals,since they are all a similar basing/pinout(7ac?).
This leaves us open to use 6L6,EL34,6550,KTxx,etc. for output tubes.
We'll have to have a -Vg1 supply with a wide voltage range to cover the needs of all those tubes,shouldn't be a problem.

The power transformer is a big 1kva/500W beast,used in the Tektronix 545A. (P/N 120-120)
Pete Millett was kind enough to post some data on this transformer,and a few others here:
Tek power transformers

The output transformers are rated ~100W,they came from a pair of old RCA MI-12188A amps.
They are ~3.5-4.0K (p-p) primary impedance.
There is some information on these amplifiers/transformers here:
The Shrine of the Ancient and Most Excellent RCA MI-12188A Power Amplifier...

Posted 2nd September 2011 at 01:00 AM by DigitalJunkie Comments 0
Posted in Uncategorized
I got this amp in 'fried' condition from a friend many years ago. I finally managed to get it working,and I've been using it for my subwoofer amp ever since,probably about 10 years now? It's not the greatest amp,but it has served me very well on sub duty.

It claims to be 200W per channel, and bridgeable to 400W. It might even pull that off,on a good day.

Anyways,I had some very poor scans of the schematic for this amp(which I later discovered was almost identical to a 4 channel Rockwood amp.) I managed to re-draw the basics,and thought I'd post it up for the forum to check out.

I've been thinking of taking this amp to the bench to do some tests,and maybe some tweaks. I'm all ears if anyone has any thoughts?

Here's a link to the redrawn schematics,I might put the original scans in there also.
Some component values are missing,I was going from memory,and what I could make out from the original scans.

MA-9400 pictures by Nothing40 - Photobucket

Posted 2nd June 2011 at 08:01 AM by DigitalJunkie Comments 0
Posted in Uncategorized
Inspired by This Thread I decided to build something similar,I've though about it before,and had some parts sitting here,so what the heck!

Amp Schematic

PSU schematic


Here's what I've got at the moment.
25BQ6GTB tubes,(re-)branded DuMont. These are the skinny 6V6-sized bottles.(11W anode rating,and ~200V screen rating)

A pair of those are driving a 3.5K PP output transformer,rated for ~100W. (came from a scrapped Bogen M120 4x PPP 8417 amp.)

Bogen Schematic

B+=457V
Va=455V
B2+/Vg2=224V
Vg1=-43V
Vk (33ohm Rk's) ~1.3V ,About 40ma/tube.
(I saw cathode current peaks of ~80ma per tube,perhaps more? hard to tell with my DMM)

That gives a dissipation of ~18W per tube. Much more current and the plates start to 'blush'.
I did *not* see any screen glow,but the mica's on these particular tubes make it kind of hard to see much inside....
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