Topics

Unknown Type 547 add-on circuit.

Martin Hodge
 

Can anyone identify the circuit shown in the photo album? It's in a Type 547 I got off craigslist for $10.

https://groups.io/g/TekScopes/album?id=250335

It's only connections are a 4 pin xlr socket mounted thru a hole in the left cowling and 4 leads that clip directly to the CRT deflection plates. Apparently some kind of interface, but for what?

snapdiode
 

I think the bigger story here is a 10$ 547.

Martin Hodge
 

Actually the total bill was $60, for a 535a, 547, 549, 575, 585a and a little Heathkit scope. I was very pleased, but the suspension on my van was not.

I was really after the 575. I'd been wanting a curve tracer and the other units were gravy. The 585a and the heathkit were unfortunately rotted away far beyond saving. But I've got the 575 and the 535a working nicely and calibrated. The 547 I've just finished but haven't calibrated yet. The 549 storage scope is going to have to wait, it needs two 8608 tubes in the vertical amp (gassy) which are very expensive.

The 535a has a beautiful, bright and razor sharp aqua colored trace and is completely transistor free when equipped with a Type 53/54K. I feel like a bolt of lightning could hit it and it would keep right on ticking.

John Williams
 

Nice buy Martin! Wow that is a dream. I checked vacuumtubes.net and they are $25 each new. I am going to check and see how many spares I have. I will let you know if I can help. John

Dave Seiter
 

A nice haul!  I have a 549 around somewhere that I've been meaning to restore; thanks for reminding me!
-Dave

On Sunday, July 12, 2020, 05:03:39 PM PDT, Martin Hodge <mhodge@...> wrote:

Actually the total bill was $60, for a 535a, 547, 549, 575, 585a and a little Heathkit scope. I was very pleased, but the suspension on my van was not.

I was really after the 575. I'd been wanting a curve tracer and the other units were gravy. The 585a and the heathkit were unfortunately rotted away far beyond saving. But I've got the 575 and the 535a working nicely and calibrated. The 547 I've just finished but haven't calibrated yet. The 549 storage scope is going to have to wait, it needs two 8608 tubes in the vertical amp (gassy) which are very expensive.

The 535a has a beautiful, bright and razor sharp aqua colored trace and is completely transistor free when equipped with a Type 53/54K.  I feel like a bolt of lightning could hit it and it would keep right on ticking.

Dave Wise
 

That was an unbelievable deal. I'd be pinching myself to prove I was not dreaming it.

That mod was available on most (all?) of the 500-series scopes, it gives direct access to the CRT vertical deflection plates so you can bypass the built-in vertical amp and drive them at frequencies far above spec with external equipment.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Martin Hodge via groups.io <mhodge=innocent.com@groups.io>
Sent: Sunday, July 12, 2020 4:17 PM
To: TekScopes@groups.io
Subject: [TekScopes] Unknown Type 547 add-on circuit.

Can anyone identify the circuit shown in the photo album? It's in a Type 547 I got off craigslist for $10.

https://groups.io/g/TekScopes/album?id=250335

It's only connections are a 4 pin xlr socket mounted thru a hole in the left cowling and 4 leads that clip directly to the CRT deflection plates. Apparently some kind of interface, but for what?

Dave Wise
 

Beware that the 547 and 549 are susceptible to a high-voltage transformer problem. Tek switched to an epoxy-based winding impregnant which has become lossy. The symptom is loss of high voltage, sometimes after a short time on the order of minutes to a couple hours. Chuck Harris is working on an industrial-grade rewinding operation, or you can try my low-tech DIY approach documented in topic and album titled "453 HV Transformer Rewind". The 547 transformer winding spec is available at TekWiki, w140.com .

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Dave Seiter via groups.io <d.seiter=att.net@groups.io>
Sent: Sunday, July 12, 2020 5:55 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Unknown Type 547 add-on circuit.

A nice haul! I have a 549 around somewhere that I've been meaning to restore; thanks for reminding me!
-Dave
On Sunday, July 12, 2020, 05:03:39 PM PDT, Martin Hodge <mhodge@...> wrote:

Actually the total bill was $60, for a 535a, 547, 549, 575, 585a and a little Heathkit scope. I was very pleased, but the suspension on my van was not.

I was really after the 575. I'd been wanting a curve tracer and the other units were gravy. The 585a and the heathkit were unfortunately rotted away far beyond saving. But I've got the 575 and the 535a working nicely and calibrated. The 547 I've just finished but haven't calibrated yet. The 549 storage scope is going to have to wait, it needs two 8608 tubes in the vertical amp (gassy) which are very expensive.

The 535a has a beautiful, bright and razor sharp aqua colored trace and is completely transistor free when equipped with a Type 53/54K. I feel like a bolt of lightning could hit it and it would keep right on ticking.

John Griessen
 

On 7/12/20 8:00 PM, Dave Wise wrote:
Can anyone identify the circuit shown in the photo album? It's in a Type 547 I got off craigslist for $10.
https://groups.io/g/TekScopes/album?id=250335

I can't get that to show in firefox or chrome. I'm logged in, but that URL redirects to https://groups.io/g/TekScopes with no mention of albums anywhere...

Chuck Harris
 

The 500 series scopes all (?) had ports on the left
side for direct connection to the deflection plates.
This allowed the user to gain faster sweeps and deflection
than was available from the scope's circuitry.

And, it had the side benefit of allowing all of the bias
circuitry, and anode voltages to be provided by the
host chassis.

For your purposes, you will probably want to remove the
modification, and reconnect the deflection wires to
the CRT.

Don't break the CRT pins sticking out of the neck.
The socket pins should slide on straight and easy.

I find that using a usual set of pliers to grip the
socket pins lets them pivot too easy, and invites
catastrophe. I have a pair of needle nose pliers that
have semi circular tips (like a piece of tubing slit
down its sides), about 3/32 inch in diameter that are
perfect for gripping the socket pins.

-Chuck Harris

Martin Hodge wrote:

Can anyone identify the circuit shown in the photo album? It's in a Type 547 I got off craigslist for $10.

https://groups.io/g/TekScopes/album?id=250335

It's only connections are a 4 pin xlr socket mounted thru a hole in the left cowling and 4 leads that clip directly to the CRT deflection plates. Apparently some kind of interface, but for what?



Morris Odell
 

Good advice from Chuck Harris about care in removing wires from the CRT pins. On a related note I once was asked to repair a 535 scope that had damaged resistors in the VA because the wires had slipped off the CRT pins and come in contact with the chassis. This destroyed the non inductive resistors in the plate loads of the output tubes. As part of the repair I put a a dab of conductive glue on the connection to make sure it couldn't happen again.

Morris

Dave Seiter
 

Yeah, I know all too well; fortunately, I only have one that's marginal, the rest of 547s are ok (so far!)  I've rewound HP solenoid coils and a few other items, but  never tried a transformer.
-Dave

On Sunday, July 12, 2020, 06:07:53 PM PDT, Dave Wise <david_wise@...> wrote:

Beware that the 547 and 549 are susceptible to a high-voltage transformer problem.  Tek switched to an epoxy-based winding impregnant which has become lossy.  The symptom is loss of high voltage, sometimes after a short time on the order of minutes to a couple hours.  Chuck Harris is working on an industrial-grade rewinding operation, or you can try my low-tech DIY approach documented in topic and album titled "453 HV Transformer Rewind".  The 547 transformer winding spec is available at TekWiki, w140.com .

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Dave Seiter via groups.io <d.seiter=att.net@groups.io>
Sent: Sunday, July 12, 2020 5:55 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Unknown Type 547 add-on circuit.

A nice haul!  I have a 549 around somewhere that I've been meaning to restore; thanks for reminding me!
-Dave
    On Sunday, July 12, 2020, 05:03:39 PM PDT, Martin Hodge <mhodge@...> wrote:

Actually the total bill was $60, for a 535a, 547, 549, 575, 585a and a little Heathkit scope. I was very pleased, but the suspension on my van was not.

I was really after the 575. I'd been wanting a curve tracer and the other units were gravy. The 585a and the heathkit were unfortunately rotted away far beyond saving. But I've got the 575 and the 535a working nicely and calibrated. The 547 I've just finished but haven't calibrated yet. The 549 storage scope is going to have to wait, it needs two 8608 tubes in the vertical amp (gassy) which are very expensive.

The 535a has a beautiful, bright and razor sharp aqua colored trace and is completely transistor free when equipped with a Type 53/54K.  I feel like a bolt of lightning could hit it and it would keep right on ticking.

Albert Otten
 

Hi John, works fine here with Firefox. In such cases I click Photos at the website and set "Sort by created" arrow down, i.e. new to old. It will be one of the first albums.
Albert

On Mon, Jul 13, 2020 at 03:11 AM, John Griessen wrote:


On 7/12/20 8:00 PM, Dave Wise wrote:
Can anyone identify the circuit shown in the photo album? It's in a Type 547
I got off craigslist for $10.

https://groups.io/g/TekScopes/album?id=250335

I can't get that to show in firefox or chrome. I'm logged in, but that URL
redirects to https://groups.io/g/TekScopes with no
mention of albums anywhere...

Roy Thistle
 

On Sun, Jul 12, 2020 at 09:24 PM, Chuck Harris wrote:


have a pair of needle nose pliers that
have semi circular tips (like a piece of tubing slit
down its sides), about 3/32 inch in diameter that are
perfect for gripping the socket pins.
If you have a chance... a pic ... or perhaps... a reasonable facsimile thereof... from Google images.. for the imaginally chalanged and CRT deflection pin breakers among us (me!)

Roy Thistle
 

On Sun, Jul 12, 2020 at 09:39 PM, Morris Odell wrote:


I put a a dab of conductive glue on the connection to make sure it couldn't
happen again.
I imagine... silver filled polyurethane?... but could of been carbon or metal? filled 2-part epoxy? Did you add a label to slow down any pliers welding pin-braking posterity?

Martin Hodge
 

I've carefully traced the topology of this board and I can say fairly certain it is not an input circuit. The crt pin leads connect through about 300k ohms of resistors to the _bases_ of NPN transistors. I've applied +-12.6v and a signal to the board at several points and the signal always shows up at the XLR plug. Sorry, but the mystery remains.

Dave, thanks for the warning regarding the hv transformers, I had read up on that before I started on the 547 and it appears to be stable at the moment. I was reading only 7600v at the anode for a while, which concerned me. But it turned out the 1M ohm resistor on the anode capacitor was open. After replacing it I had the expected 8200v.

The 549 hv circuit went out with a bang before I got it. The 220ohm 2w resistor on the primary side of the transformer was exploded and charred the inside of the housing. It looks like the driver tube, a 6gf5 if I remember, popped and shorted out the resistor. Replacing both the tube and resistor brought back the hv circuit with good voltage readings and a nice bright trace. The storage circuit appears to be working. I can draw on the tube with the horizontal and vertical position knobs like an etch-a-sketch and press the erase buttons to clear it. Both sweeps on the 549 are stuck in hold off though.

The 547 sweep 'b' had the same issue. The problem there was the 5.9meg resistor to ground on the grid of the first stage of the hold off circuit had opened. A 4.7m + 1.2m in series to replace it was all that was needed to get it running again. These scopes are so easy to repair I'm confident I can get the 549 running again if I can get ahold of those 8608 tubes.

John, that's very kind and generous of you! I dont mind paying a reasonable price + postage for those tubes if you have them. Thank you!

John Gord
 

Martin,
From what I can see of the board, it may be an output buffer board: It may provide deflection-voltage-derived X and Y output to some external device, probably at fairly low bandwidth.
--John Gord

On Mon, Jul 13, 2020 at 05:49 PM, Martin Hodge wrote:


I've carefully traced the topology of this board and I can say fairly certain
it is not an input circuit. The crt pin leads connect through about 300k ohms
of resistors to the _bases_ of NPN transistors. I've applied +-12.6v and a
signal to the board at several points and the signal always shows up at the
XLR plug. Sorry, but the mystery remains.

Dave, thanks for the warning regarding the hv transformers, I had read up on
that before I started on the 547 and it appears to be stable at the moment. I
was reading only 7600v at the anode for a while, which concerned me. But it
turned out the 1M ohm resistor on the anode capacitor was open. After
replacing it I had the expected 8200v.

The 549 hv circuit went out with a bang before I got it. The 220ohm 2w
resistor on the primary side of the transformer was exploded and charred the
inside of the housing. It looks like the driver tube, a 6gf5 if I remember,
popped and shorted out the resistor. Replacing both the tube and resistor
brought back the hv circuit with good voltage readings and a nice bright
trace. The storage circuit appears to be working. I can draw on the tube with
the horizontal and vertical position knobs like an etch-a-sketch and press the
erase buttons to clear it. Both sweeps on the 549 are stuck in hold off
though.

The 547 sweep 'b' had the same issue. The problem there was the 5.9meg
resistor to ground on the grid of the first stage of the hold off circuit had
opened. A 4.7m + 1.2m in series to replace it was all that was needed to get
it running again. These scopes are so easy to repair I'm confident I can get
the 549 running again if I can get ahold of those 8608 tubes.

John, that's very kind and generous of you! I dont mind paying a reasonable
price + postage for those tubes if you have them. Thank you!

snapdiode
 

Maybe for driving an x-y plotter?

John Williams
 

Hi Martin. I see I have 4 of the little buggers and there seems to be only 2 in the 549. If you use my email address books4you4 at mail dot com I will test them and send you a pair. Stay safe. John

Morris Odell
 

I imagine... silver filled polyurethane?... but could of been carbon or metal?
filled 2-part epoxy? Did you add a label to slow down any pliers welding
pin-braking posterity?
I don't think it was anything as fancy as that. It was some black goo sold labelled 'conductive glue' by the local electronics emporium down here in Australia. It should be pretty obvious to the naked eye so so no label.

Chuck Harris
 

Just imagine a pair of pointed pliers where when the points
are closed, they form a tube about 3/32" in diameter, and
1/4" long.

-Chuck Harris

Roy Thistle wrote:

On Sun, Jul 12, 2020 at 09:24 PM, Chuck Harris wrote:


have a pair of needle nose pliers that
have semi circular tips (like a piece of tubing slit
down its sides), about 3/32 inch in diameter that are
perfect for gripping the socket pins.
If you have a chance... a pic ... or perhaps... a reasonable facsimile thereof... from Google images.. for the imaginally chalanged and CRT deflection pin breakers among us (me!)