Hickok 1805A - Tek 545 clone - circuit anomolies - UK Vintage Radio Repair and Restoration Discussion Forum

Diabolical Artificer · 13th Dec 2019, 10:11 am

I've one of the above on the bench, it's working ish, IE got a trace and most controls work, but in an effort to get to grips with it I need to check voltages etc. I've been unable to find a 1805A service manual, so am using the 545A and 545 manuals,however some component values are different to the Tek 545 as are valves designations which makes finding TP's difficult.

For instance I'm starting to look at the -150v supply, every other supply uses this as a reference, but the Tek 545 manual has the 5651 as V710, the 545A has it as V609, same with the ECC83, but what is more disconcerting is that the 470k anode resistor shown in both is nowhere to be found. I'm pretty damn sure its a 270k on this Hickok 1805A, making finding a test point to check if I have -85/87v tricky.

Does anyone know for certain which Tek scope the 1805A is a clone of?

Andy.

Andrewausfa · 13th Dec 2019, 10:17 am

Morning Andy,

http://w140.com/tekwiki/images/1/18/...schematics.pdf

Andrew

Diabolical Artificer · 13th Dec 2019, 4:55 pm

Thanks, that'll make life easier, looked for ages but couldn't find anything.

A

Chris55000 · 18th Dec 2019, 1:42 am

Evening Andy!

Judging from the fuss made by Tek and the U.S. about Hickok plagiarising their 545A, I think you'll find they've probably copied it right down to the row of marked h.t. supply test points along one side of the bottom chassis, as well as wiring colours, so have a look for wiring coloured White–Green–Black – I think you'll find that that's the colour code for the –150V stabilized h.t. rail!

I did write some fault–finding notes in reference to the operation of the h.t. stabilizer V609 on the EEV Blog Forum in reply to a Member there who had missing traces on a '755, and he said the –150V line measured –270V on his instrument!

The most important thing with this circuit is that there should be no flickering or unsteadiness of the glow in the neon regulator tube, (please see "Neons In the Experimenter's Power Pack" by Martin Michaelis, P.W., July 1962) – any flickering may indicate parasitic relaxation oscillation may be occurring, which would be amplified by the control amplifier valve and cause havoc throughput the 'scope generally, if you find any, replace V609 with a new one and check R608!

If I can be of help with spares, please PM me – I have one of these!

Chris Williams

Diabolical Artificer · 18th Dec 2019, 7:33 am

Thanks Chris, the scope is working though there are a few issues like drifting of the B trace, one Hor control doesn't work as well as other minor issues. The main problem though is when I come to start it in the morning, I get arching on one cap in the doubler 8kv circuit to chassis.

I stripped the EHT section down as it was covered in oil and crap, where the oil came from I've no idea. Both tfmr and caps look and test ok. This worked till next power up, so I went for liberal application of red nail varnish on all HV/EHT points/joints and thick tape on the chassis, oh and I stuck it in front of the fire, but my workshop is cold and a bit damp, not ideal.

I checked the -150v and that section of the PSU checks out, however there's a wafer on the top RHS with voltages written on, all are high, that said it's hard to know what section of the ceramic wafer is refered to, there's no arrow. I'll check the colour coding of the wire and re-read the 545 manual. Thanks for the tip re the reference valve and neons which do flash.

Thanks for your help, Andy.

Chris55000 · 18th Dec 2019, 12:10 pm

Hi!

No problems Andy! Please keep us posted!

I know the e.h.t. section of my 545A works fine without any fireworks, so if I can assist with bits & pieces, please PM me!!!!

Chris Williams

Diabolical Artificer · 21st Dec 2019, 10:38 am

I've managed to tame the EHT section, no arcing and fireworks on startup, but whilst testing last night I noticed a valve with a blue glow. This explains why the timebase has always been a bit iffy. The Hor control only works on one pot and the sweep sometimes takes a while to kick in.

The valve in question is a 6BA8A triode pentode, at first I thought I might be abl to sub a ECF/L80 or similar, but pinout is different. I did find a 6EB8 which is similar but doesn't work, so I'll need to send off for one to the states. I,ve noticed that the neons flicker as you mentioned Chris, maybe this duff valve is the cause? See att schematic 6BA8A is at the bottom.

Andy.

Chris55000 · 23rd Dec 2019, 2:30 pm

Afternoon Andy!

I can post one from mine to you after I get back from Holliers on the 29th – If there's anything you'd like me to dig out of my 545a please PM me!

Any valve with a blue glow in the space between electrodes in it is definitely suspect, however don't confuse this with internal fluorescence, which is on the inside surfaces of the glass and anode surfaces, etc!

Internal Fluorescence is harmless, often jumps about in a completely haphazard fashion, and sometimes alters with different control settings, etc!

Chris Williams

Chris55000 · 23rd Dec 2019, 2:33 pm

PS!

I've just had a look at your pic and that valve definitely looks like a bin job to me!

I'll get one from mine sorted out and posted to you after my Holliers!

Chris Williams

Diabolical Artificer · 25th Dec 2019, 6:50 am

Thanks Chris does the 545A have one? The 545B doesn't. Don't want to nick a valve from a working scope though. Am going through the manual and scope at present so will let you know how I get on, need to print the manual off as reading off a screen is less than optimal.

Andy.

13th Dec 2019, 10:11 am	#1
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Hickok 1805A - Tek 545 clone - circuit anomolies I've one of the above on the bench, it's working ish, IE got a trace and most controls work, but in an effort to get to grips with it I need to check voltages etc. I've been unable to find a 1805A service manual, so am using the 545A and 545 manuals,however some component values are different to the Tek 545 as are valves designations which makes finding TP's difficult. For instance I'm starting to look at the -150v supply, every other supply uses this as a reference, but the Tek 545 manual has the 5651 as V710, the 545A has it as V609, same with the ECC83, but what is more disconcerting is that the 470k anode resistor shown in both is nowhere to be found. I'm pretty damn sure its a 270k on this Hickok 1805A, making finding a test point to check if I have -85/87v tricky. Does anyone know for certain which Tek scope the 1805A is a clone of? Andy. Attached Thumbnails __________________ Curiosity hasn't killed this cat...so far.

13th Dec 2019, 10:17 am	#2
Andrewausfa Octode Join Date: Dec 2010 Location: St Ives, Cambridgeshire, UK. Posts: 1,180	Re: Hickok 1805A - Tek 545 clone - circuit anomolies Morning Andy, http://w140.com/tekwiki/images/1/18/...schematics.pdf Andrew __________________ Invisible airwaves crackle with life. Or they should do. BVWS Member

13th Dec 2019, 4:55 pm	#3
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: Hickok 1805A - Tek 545 clone - circuit anomolies Thanks, that'll make life easier, looked for ages but couldn't find anything. A __________________ Curiosity hasn't killed this cat...so far.

18th Dec 2019, 1:42 am	#4
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,868	Re: Hickok 1805A - Tek 545 clone - circuit anomolies Evening Andy! Judging from the fuss made by Tek and the U.S. about Hickok plagiarising their 545A, I think you'll find they've probably copied it right down to the row of marked h.t. supply test points along one side of the bottom chassis, as well as wiring colours, so have a look for wiring coloured White–Green–Black – I think you'll find that that's the colour code for the –150V stabilized h.t. rail! I did write some fault–finding notes in reference to the operation of the h.t. stabilizer V609 on the EEV Blog Forum in reply to a Member there who had missing traces on a '755, and he said the –150V line measured –270V on his instrument! The most important thing with this circuit is that there should be no flickering or unsteadiness of the glow in the neon regulator tube, (please see "Neons In the Experimenter's Power Pack" by Martin Michaelis, P.W., July 1962) – any flickering may indicate parasitic relaxation oscillation may be occurring, which would be amplified by the control amplifier valve and cause havoc throughput the 'scope generally, if you find any, replace V609 with a new one and check R608! If I can be of help with spares, please PM me – I have one of these! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed! Last edited by Chris55000; 18th Dec 2019 at 1:48 am.

18th Dec 2019, 7:33 am	#5
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: Hickok 1805A - Tek 545 clone - circuit anomolies Thanks Chris, the scope is working though there are a few issues like drifting of the B trace, one Hor control doesn't work as well as other minor issues. The main problem though is when I come to start it in the morning, I get arching on one cap in the doubler 8kv circuit to chassis. I stripped the EHT section down as it was covered in oil and crap, where the oil came from I've no idea. Both tfmr and caps look and test ok. This worked till next power up, so I went for liberal application of red nail varnish on all HV/EHT points/joints and thick tape on the chassis, oh and I stuck it in front of the fire, but my workshop is cold and a bit damp, not ideal. I checked the -150v and that section of the PSU checks out, however there's a wafer on the top RHS with voltages written on, all are high, that said it's hard to know what section of the ceramic wafer is refered to, there's no arrow. I'll check the colour coding of the wire and re-read the 545 manual. Thanks for the tip re the reference valve and neons which do flash. Thanks for your help, Andy. __________________ Curiosity hasn't killed this cat...so far.

18th Dec 2019, 12:10 pm	#6
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,868	Re: Hickok 1805A - Tek 545 clone - circuit anomolies Hi! No problems Andy! Please keep us posted! I know the e.h.t. section of my 545A works fine without any fireworks, so if I can assist with bits & pieces, please PM me!!!! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

21st Dec 2019, 10:38 am	#7
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: Hickok 1805A - Tek 545 clone - circuit anomolies I've managed to tame the EHT section, no arcing and fireworks on startup, but whilst testing last night I noticed a valve with a blue glow. This explains why the timebase has always been a bit iffy. The Hor control only works on one pot and the sweep sometimes takes a while to kick in. The valve in question is a 6BA8A triode pentode, at first I thought I might be abl to sub a ECF/L80 or similar, but pinout is different. I did find a 6EB8 which is similar but doesn't work, so I'll need to send off for one to the states. I,ve noticed that the neons flicker as you mentioned Chris, maybe this duff valve is the cause? See att schematic 6BA8A is at the bottom. Andy. Attached Thumbnails __________________ Curiosity hasn't killed this cat...so far.

23rd Dec 2019, 2:30 pm	#8
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,868	Re: Hickok 1805A - Tek 545 clone - circuit anomolies Afternoon Andy! I can post one from mine to you after I get back from Holliers on the 29th – If there's anything you'd like me to dig out of my 545a please PM me! Any valve with a blue glow in the space between electrodes in it is definitely suspect, however don't confuse this with internal fluorescence, which is on the inside surfaces of the glass and anode surfaces, etc! Internal Fluorescence is harmless, often jumps about in a completely haphazard fashion, and sometimes alters with different control settings, etc! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

23rd Dec 2019, 2:33 pm	#9
Chris55000 Nonode Join Date: Aug 2007 Location: Walsall Wood, Aldridge, Walsall, UK. Posts: 2,868	Re: Hickok 1805A - Tek 545 clone - circuit anomolies PS! I've just had a look at your pic and that valve definitely looks like a bin job to me! I'll get one from mine sorted out and posted to you after my Holliers! Chris Williams __________________ It's an enigma, that's what it is! This thing's not fixed because it doesn't want to be fixed!

25th Dec 2019, 6:50 am	#10
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,658	Re: Hickok 1805A - Tek 545 clone - circuit anomolies Thanks Chris does the 545A have one? The 545B doesn't. Don't want to nick a valve from a working scope though. Am going through the manual and scope at present so will let you know how I get on, need to print the manual off as reading off a screen is less than optimal. Andy. __________________ Curiosity hasn't killed this cat...so far.