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Old 20th Jun 2020, 1:33 pm   #1
AndyWright
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Default Labgear Topbander

I've acquired a Labgear topbander transmitter which needs restoration. I know there were 2 variants of this, I suspect I have the latter.

The original MK1, whose circuit is readily available on the net shows a modulator valve line up of EF80, 12AU7 and 12BH7.

The version I have, has a modulator valve line up of EF80 (mic amp) followed by an ECL82 (triode pentode) and another valve (definitely not a double triode or an ECL82) which has lost its markings. Some of the wiring around the mod section has been disrupted.

Does anyone have the schematic for what I presume is the MK2 version of this transmitter?

Cheers

Andy G4OJY
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Old 20th Jun 2020, 5:27 pm   #2
AndyWright
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Default Re: Labgear Topbander

I've made a little progress. The topbander manual djvu file on boat anchor manual archive mentions the modulator valve line up as EF80, ECL82 and EL84, so I guess this is what I have. There is no schematic with this manual, but the manual for the labgear LG160 does have a crude schematic with an EL84 modulator.

At least I can now try and retrace the schematic knowing what the valve line up in the mod is.
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Old 20th Jun 2020, 11:44 pm   #3
m0cemdave
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Default Re: Labgear Topbander

I have the circuit diagram for that version (stated as for use with transmitter serial numbers prefixed "S" only).
I need to scan it in sections and stitch them together.

Also the relevant manual, a bit yellow with age but will probably clean up OK.

Watch this space...
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Old 21st Jun 2020, 8:30 am   #4
AndyWright
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Default Re: Labgear Topbander

Thanks Dave that will be really useful.

Andy
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Old 21st Jun 2020, 2:02 pm   #5
m0cemdave
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Default Re: Labgear Topbander

Here is the circuit. It will be compressed by the forum software, so if it's not readable I will try again.

edit:
Not readable on the forum, but I can send the file to you if you PM me an email address (don't post it here).

Last edited by m0cemdave; 21st Jun 2020 at 2:28 pm.
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Old 21st Jun 2020, 2:28 pm   #6
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Default Re: Labgear Topbander

If you can convert it to a .pdf file the forum accepts these up to 4M.
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Old 22nd Jun 2020, 11:58 am   #7
ribbonmicsrus
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Default Re: Labgear Topbander

Dave
Can I ask a favour as well, can you send me a copy as well, mine is working well but it would be nice to have for reference.

73
Andy G3UEQ
QTHR QRZ.com
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Old 22nd Jun 2020, 10:14 pm   #8
m0cemdave
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Default Re: Labgear Topbander

The Topbander Mk2 manual:
These pages are all readable on here, but if anyone wants a higher resolution copy for printing etc please send me a PM with an email address.
(see next message for the last two pages)
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Last edited by m0cemdave; 22nd Jun 2020 at 10:23 pm.
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Old 22nd Jun 2020, 10:15 pm   #9
m0cemdave
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Default Re: Labgear Topbander

last pages:
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Last edited by m0cemdave; 22nd Jun 2020 at 10:20 pm.
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Old 22nd Jun 2020, 10:16 pm   #10
m0cemdave
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Default Re: Labgear Topbander

Andy (ribbon mics), you have a PM.
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Old 23rd Jun 2020, 5:39 am   #11
G3VKM_Roger
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Default Re: Labgear Topbander

Hi All,

I put the MK1 manual on BAMA many moons ago, see here:-

http://bama.edebris.com/manuals/labgear/topbander

Unfortunately, I didn't own a MK2 and so have never chased up the manual for that mark. If a copy is located could the finder please add it to the BAMA directory and let the group know?
73

Roger/G3VKM
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Old 28th Jun 2020, 4:41 pm   #12
AndyWright
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Default Re: Labgear Topbander

I've finally got the tx up and running. Can anyone with the MK2 version comment on how much output power they are getting. Into a 50 ohm load I get just under 5 watts. PA anode current is about 35mA dipped in the CW position.

I cannot get more than 1mA of grid current even with the drive pot on max, though the manual says I should be able to get at least 2.5mA

I have peaked L3 for max grid current.

Cheers

Andy
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