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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 25th Apr 2019, 5:30 pm   #1
Dorian27
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Default Elizabethan LZ-29

Can any one tell me where I could get one of these please it is a Westinghouse EC1 U567 thank you
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Old 25th Apr 2019, 5:57 pm   #2
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Default Re: Rectifier

Use a silicon bridge rectifier of a suitable rating with a series resistor to make the rectified output voltage correct.
A selection at this web site but many other suppliers.

https://uk.rs-online.com/web/c/semic...ge-rectifiers/
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Old 25th Apr 2019, 6:14 pm   #3
Dorian27
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Default Re: Rectifier

Not sure how to do this but thanks
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Old 25th Apr 2019, 6:30 pm   #4
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Default Re: Rectifier

Well there is no point in trying to find a NOS (New Old Stock) Westinghouse rec as it will be past its best and won't be reliable. I'm sure we can help you wire in a suitable silicon bridge rectifier if we have more information on the item you are restoring/repairing. It's not difficult...just requires care to get the four connections correct. So some good pictures of what you have and the model number of the item and we can then give practical advice on a suitable silicon rec replacement and how to go about wiring it in place of the Westinghouse.

The connections are clearly marked on the original and similar markings will be shown on the replacement....so it should be dead easy!
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Old 25th Apr 2019, 6:30 pm   #5
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Default Re: Rectifier

What is it out of? Please don't be tempted to buy a "good" second hand one, it will not last very long.


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Old 25th Apr 2019, 10:42 pm   #6
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Default Re: Rectifier

Hy thanks all for your help the rectifier is out of ELIZABETHAN LZ-29
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Old 25th Apr 2019, 11:22 pm   #7
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Default Re: Rectifier

Here are pictures I took before dissmantlin the rectifier The pictures after dissmantlin are further up on another thread hope they help thanks
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Old 25th Apr 2019, 11:27 pm   #8
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Default Re: Rectifier

Have you got the circuit? if not its available top right of this page for 1.99. The rectifier should be bolted to the chassis, it acts as a heat sink. Where the circuit points to 270 near MR1 that wire need cutting and a resistor inserting, maybe 200 ohms 5W also bolted to the chassis to dissipate the heat. Exact value not critical but should be chosen to get near the 270V indicated. Once you have that sorted consider changing MR2 in the magic eye circuit an ordinary Silicon Diode, the 100k resistor may need increasing.


John.

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Old 26th Apr 2019, 7:07 am   #9
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Default Re: Rectifier

Replace Bridge Rectifier as suggested above, any 400v 1A or above rated Bridge Rectifier will do or nick one out of a PC ATX PSU but check the datasheet first, the Bridge Rectifier's datasheet that is.

After the Bridge Rectifier between HT and + of the BR pop a big 5W low value resistor from your parts stash, 200 - 270r as suggested above or to start use a 100r. Clip your voltmeter leads either side of the resistor and switch the set on briefly but long enough for it to warm up. Divide the voltage reading by the resistor value to get the I or current, it should be around 100mA or below broadly speaking. From the schematic find out what HT should be then divide this figure by I (current) to get what value R you need, no need to get bang on as long as it's +/- 10v or so it'll be right.

Fit new R and then check HT is on spec. One other thing the schematic value will probably have been measured with an Avo or similar, so HT as measured with a DMM will be higher. Not sure if there is a rule of thumb to help figure the HT value as measured by a DMM, add 20v perhaps? Others here will know.

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Old 26th Apr 2019, 9:23 am   #10
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Default Re: Rectifier

Extract from circuit attached.
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Old 26th Apr 2019, 11:03 am   #11
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Default Re: Rectifier

Andy #9
The resistor voltage drop will be higher than what Mr Ohm would say because the current comes in pulses. The resistor dissipation would also be higher than that calculated from a steady current.

The meter voltage error will depend on the meter resistance and the source resistance. I would think that there would be very little error when measuring the HT voltage with a low source resistance.
Some cheap digital meters have an input resistance of 1M which is the lower than an analog meter 20k/V on the 1kV range. Posher digital meters have an input resistance of 10M. The error can be calculated if you are so inclined.
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Old 26th Apr 2019, 11:52 am   #12
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Default Re: Rectifier

Would a 400 PRRV be good enough? I would have gone for one at least twice that rating, the price is little different for a 1000v one and they are similar in size.
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Old 26th Apr 2019, 12:08 pm   #13
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Default Re: Rectifier

Out of interest:

https://www.kevinchant.com/uploads/7...placements.pdf

Lawrence.
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Old 26th Apr 2019, 1:50 pm   #14
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Default Re: Rectifier

Am I missing something here? If you are replacing one semiconductor bridge with another why should any new series resistor need to be added?.
If the original component was selenium it might be necessary as the Vf would be higher but replacing a germanium with silicon would make very little difference. The original appears to have the connections marked so replacement with one of any number of devices should be quite straightforward. Unless "authenticity" is the objective I would have thought that any 1000v piv 2amp bridge would suffice and provide more than adequate safety margins. (I am guessing about a suitable current rating being unfamiliar with demands of the actual circuit). The circuit shown appears to have a 270v HT after the bridge, this would seem to indicate an rms input voltage from the transformer of approximately 195v. The minimum piv rating for the bridge should therefore be 550 volts. (All figures are approximate)

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Old 26th Apr 2019, 6:33 pm   #15
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Default Re: Rectifier

I believe the original component is selenium, what makes you think it is germanium?
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Old 26th Apr 2019, 6:41 pm   #16
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Default Re: Rectifier

Thanks all for your help but I think this is to much for me I will leave it unless I can get similar with not much to do to replace . I don't think I am capable of doing all that I am an amiture at this and don't want to make things worse.i thought I could get a straight equivalent replacement.
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Old 26th Apr 2019, 6:44 pm   #17
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Default Re: Rectifier

There may be someone nearby who can show you if you ask around. It’s a very simple change but appreciate it seems much more if you have not repaired this type of item before.
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Old 26th Apr 2019, 9:07 pm   #18
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Default Re: Rectifier

Quote:
Originally Posted by Dorian27 View Post
i thought I could get a straight equivalent replacement.
These rectifiers haven't been available for 50 years. What makes you think the existing rectifier is faulty anyway? Is the voltage output low? Is it just a guess?
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Old 26th Apr 2019, 10:14 pm   #19
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Default Re: Rectifier

My very limited experience has been that selenium rectifiers go high forward resistance but would be OK in the reverse direction.
You could try to leave the existing bridge in place and connect a W08 (1.5A 800V) bridge across it. W08 Bowood electronics 30p. If things get hot, then remove the selenium rectifier and make a tag strip for the W08.
You could open the can and put four 1N4007 or UF4007 diodes inside. (1A 1kV)
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Old 27th Apr 2019, 2:02 am   #20
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Default Re: Rectifier

Looking at the circuit, it doesn't actually make any difference which terminal the recommended additional resistor goes in series with.
The original has 5 terminals, marked with symbols, two of which (both -) are linked with a wire, so are effectively both the same, and everything connected to them goes to the (-) of the new one (via the resistor if you choose not to put it in series with one of the other legs). A replacement has 4 terminals, marked with the same symbols.
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