Re: - Circuit for the Coutant HTD1 PSE module - Circuit Please

Michael O'Beirne

This is way off topic but some of the talented bunch here may be able to help.
I have a semi unused Coutant HTD1 PSU module.  It supplies 2 x 12V stabilised outputs at around 2A max.  Some versions have an additional PCB which supplies 5V at 6A.  Google so far does not point the way to a circuit.  Does anyone here have a copy?
It’s built on an open ali chassis 11 x 4.5 x 2.5 inches deep and the technology looks to be about 1980.  So, suitably old!

From: David_Dunlop
Sent: Sunday, December 29, 2019 5:03 PM
Subject: Re: [wireless-set-no19] Tektronix Type 545 A Oscilloscope Resurrection
I have been remiss in updates I fear.

The cooling fan was reconnected and a very successful transplant of the HV Supply from the 585 A to my 545 A was performed. The moment of truth came with connecting up the power cord and throwing the switch. The first three good signs were the fuse did not blow, the indicator lamp lit and the fan came to life. A quick check of the graticule illumination proved it was working also.

On the odd side, however, I noticed the filaments in the five rectifier tubes of the HV Supply lit straight away. Was not expecting that. After 30 seconds or so, the relay tripped in and full voltage was applied to everything. Straight away, the V862 rectifier that provides 1,350 volts to the CRT cathode dimmed out and the first stage voltage tripler rectifier really lit up. A warm varnish smell also became evident from the T801 HV transformer. Worst of all, although the filaments of the CRT came up OK, no trace, and there was a lot of electrical crackling sounds coming from underneath the supply area to which the rectifiers were in sync with. Power off time.

A quick check of the 6AU5 oscillator showed it was in excellent shape, however, one half of the 12AU7 that provides regulation feedback to the oscillator had failed. Swapped it out for a new one and tried again. The crackling has disappeared and the rectifiers were now stable and that was the extent of the improvements.

A closer inspection of a series trio of resisters connected to V862 showed a value of only 6.9 Ohms. Should have been 14.1 Ohms. Way too much voltage getting through, which explained a lot. The two resister trios in my Spare HV Supply’s were giving correct values but the little sucker was tucked under the rectifier tubes on the HV Supply Board. Luckily, a chap in Toronto had 10 NOS 5642’s for sale, so I ordered them and they arrived last week.

It took two hours yesterday afternoon to pull the old rectifier tubes and replace the resister set, and then install the new 5642’s. Then the moment of truth. This time on power up, the rectifier tubes all stayed dormant until the power relay kicked in. They then seemed to be performing normally, with just the first stage tube in the HV Voltage tripler showing a bit more glow than the other two. And...with a slight adjustment of the trace controls to bring it in view, the trace was back and responding to instructions. Also more warm varnish smell from the HV Transformer.

Now some further reading is in order. A few things I can see suggest further tweaking is needed in probably the Type CA Plug In Module and the internal Calibrator of the scope itself. Let the progress continue!


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