Welcome to Australia's only Vintage Radio and Television discussion forums. You are not logged in. Please log in below, apply for an account or retrieve your password.
Australian Vintage Radio Forums
  Home  ·  About Us  ·  Discussion Forums  ·  Glossary  ·  Outside Links  ·  Policies  ·  Services Directory  ·  Safety Warnings  ·  Tutorials

Tech Talk

Forum home - Go back to Tech talk

 Help in identifying a Chassis make and model
« Back · 1 · 2 · 3 · Next »
 Return to top of page · Post #: 1 · Written at 7:43:23 PM on 14 January 2017.
Scotty's Gravatar
 Location: Melbourne, VIC
 Member since 26 December 2010
 Member #: 794
 Postcount: 328

Hi Folks,

I am currently repairing what I think is a Precedent radiogram - the cabinet is stamped Precedent but the chassis has no identifying branding or model numbers on it at all. It looks like it has been modified over the years and if I can find a schematic, I'll put it back to original. I'm guessing the valves are correct and in the correct location.

The valve lineup is as follows:
6V4
Unknown valve (looks like a 6BH5 but not really sure) it's the power amp tube
6BD7
6N8
6AN7

There is no audio from the radio at this stage but when phono is selected, there is a signal.

Radiogram Chassis
Radiogram Chassis


Thanks advance.
Scott


 
 Return to top of page · Post #: 2 · Written at 8:06:29 PM on 14 January 2017.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

With that lineup, the power amp was often a 6M5, or maybe 6AQ5.


 
 Return to top of page · Post #: 3 · Written at 8:11:32 PM on 14 January 2017.
Scotty's Gravatar
 Location: Melbourne, VIC
 Member since 26 December 2010
 Member #: 794
 Postcount: 328

That was what my thought is too - the valve that is there is not the same size as a 6M5 and the socket wouldn't take a 6AQ5. I thought (briefly) about putting a 6M5 in but didn't want to risk damage to the the unit or the valve.

Thoughts?

Cheers


 
 Return to top of page · Post #: 4 · Written at 10:23:27 PM on 14 January 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

6BH5 is an RF valve, 6M5 is a 9 pin; 6AQ5 is a 7 pin with a trap; 6BD7 & 6N8 are RF and both have two diodes N8 is more likely IF.

I would not bother fault finding nor turning it on again. There looks like there are deficiencies in the anchorage of the mains cable and that will need sorting. The focus of the photo is extremely poor. Rethink how you took it. Fixed focus cameras are a problem.

I cannot easily see what the two big caps are left of the big red ones but if there are two sets of polarised caps (electrolytic) they all have to go: Paralleling old with new with them is a no no. It has paper caps and they have to go as well and could well be the problem?

Therefore from experience I consider fault finding with that lot still in there, an exercise in futility and time wasting. The time is better spent replacing those, past their use by date, now unreliable parts.

Blunt, but I fix them commercially, time is customers money. Paper caps are replace on sight, rarely are they now not leaking or shorted.

I also check resistors as I replace caps; they go high. Some cannot be accurately measured "in circuit" but if its high in circuit it has likely failed.

We may need to check transformer voltages (rectifier removed).

After that you fault find if its still got an issue.

See if you can identify the pin outs of the valve. Look for numbers on the chassis & dates on transformers etc.

I will see if I can identify the circuit?

Marc


 
 Return to top of page · Post #: 5 · Written at 10:55:16 PM on 14 January 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

I am leaning toward President (Tasma) The chassis is not the same as M51 & M54 but AORSM stops at 1955. That circuit may be the same with a different layout?

One can compare.

Marc


 
 Return to top of page · Post #: 6 · Written at 11:27:45 PM on 14 January 2017.
Scotty's Gravatar
 Location: Melbourne, VIC
 Member since 26 December 2010
 Member #: 794
 Postcount: 328

Thanks Marc,
My intension is to replace al the caps etc as you have suggested - trouble is, not knowing what the circuit is and what the correct valve is for the audio out stage, I am not able to proceed further. The pics that were loaded are a lot clearer than they appear on the site here - if you like, I can email them to you directly.

Let me know

Cheers
Scott


 
 Return to top of page · Post #: 7 · Written at 11:53:13 PM on 14 January 2017.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

A missing valve with a known function such as power amp can often be narrowed down or guessed at by looking at the socket's connections.


 
 Return to top of page · Post #: 8 · Written at 11:56:14 PM on 14 January 2017.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 6172

I am leaning toward President (Tasma)

In which case it's likely meant to be a 6M5.


 
 Return to top of page · Post #: 9 · Written at 9:07:17 AM on 15 January 2017.
Scotty's Gravatar
 Location: Melbourne, VIC
 Member since 26 December 2010
 Member #: 794
 Postcount: 328

Hi again guys,
I had a look at President Tasma this morning and the valve line up matches models M54 and M55. Both show 6M5 as the valve I'm trying to identify. What I need to find now is a schematic for either M54 or M55 so I can make sure the correct Caps etc are installed and that no changes were made to the valve socket wiring where 6M5 is to go.
Scott


 
 Return to top of page · Post #: 10 · Written at 10:32:08 AM on 15 January 2017.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 4506

Pin outs & data can be found on Franks Electron tube pages.

6M5 pentode I suspect is recycled into several other valves.

Pin 1, g2; pin 2, g1; pin3, k & g3; pin 4, h; pin 5, h, pin 6, IC; pin 7, A; pin 8, IC, pin 9, NC. Read base / socket wiring side, clockwise

What you have to watch out for is other things on the dead pins (tags of convenience) they can be confusing.

6M5 was supposed to be getting scarce? What I have done when I could not get one is to use 6CK6 Video Output, specs suggest its the same animal. The difference is that 6CK6 has the suppressor grid on pin 6, not internally connected like 6M5.

I have changed the wiring on my sets so that I can use either in mine: Just clear pin 6 & tie it to the cathode pin.

Probably the photo of the pan is the most useful. That set has had little work done on it.

If you want I can probably get circuits. Kevin Chant has a few on his website.

Marc


 
 Return to top of page · Post #: 11 · Written at 10:51:54 AM on 15 January 2017.
Scotty's Gravatar
 Location: Melbourne, VIC
 Member since 26 December 2010
 Member #: 794
 Postcount: 328

Thanks Marc,

Have emailed you the pics plus an extra one of the valve socket (component side)

Cheers
Scott


 
 Return to top of page · Post #: 12 · Written at 11:10:44 AM on 15 January 2017.
Gandhn's Gravatar
 Location: Cameron Park, NSW
 Member since 5 November 2010
 Member #: 770
 Postcount: 351

The circuit is in AORSM and a copy sent to your email inbox.
Harold


 
 Return to top of page · Post #: 13 · Written at 11:13:59 AM on 15 January 2017.
Scotty's Gravatar
 Location: Melbourne, VIC
 Member since 26 December 2010
 Member #: 794
 Postcount: 328

Thanks Harold - I have not heard of AORSM before...
Scott


 
 Return to top of page · Post #: 14 · Written at 11:18:55 AM on 15 January 2017.
Scotty's Gravatar
 Location: Melbourne, VIC
 Member since 26 December 2010
 Member #: 794
 Postcount: 328

Just worked out what it meant - Smile


 
 Return to top of page · Post #: 15 · Written at 11:32:14 AM on 15 January 2017.
Scotty's Gravatar
 Location: Melbourne, VIC
 Member since 26 December 2010
 Member #: 794
 Postcount: 328

Hi Harold,

Have emailed you privately regarding the chassis,

Cheers
Scott


 
« Back · 1 · 2 · 3 · Next »
 You need to be a member to post comments on this forum.

Sign In

Username:
Password:
 Keep me logged in.
Do not tick box on a computer with public access.