PET 4032 replacement CRT (9 inch)

[gr8bit]

Hi everyone, new here! I have been into retro/vintage computers ever since they weren't retro/vintage I have quite a lot of the usual Commodores - 64s, Vic-20s, various peripherals, but one I didn't have was a PET. So one came up on eBay for reasonable money, and didn't require ANY work, and so I bought it. It was a long way away (Scotland) so the seller posted it.

Imagine my disappointment when it arrived broken. It had not been packed well, and the screen took a knock - probably due to being dropped by the courier - which resulted in the very end of the tube neck being broken. When turned on there is a little lighning display at the back of the monitor.

So I'm looking for a replacement tube. The one in the PET is an 9" Amperex (Philips) M24-302 GH. I have been offered a M24-306W/P, which I think is mostly the same, but would be white phosphor rather than green. Can anyone tell me if this is a drop-in (excuse the unfortunate imagery) replacement?

 

[Hugo Holden]

It is always very very sad when a CRT gets broken.

I have one M24-302GH variant and some 302W's as new old stock in my CRT collection, I will have to check. They were costly to acquire and land in Australia. Unfortunately these sorts of things are out of stock with suppliers nowadays.

As you may know, nobody has been able to rebuild CRT's for over a decade, and no new ones are being made either. They have become quite precious things now, especially unused ones.

you could PM me.

The MW24-306 sounds like a good bet, just a matter of looking up the data sheets of the two CRT's to check compatibility. Usually the guns are not the issue and can be adapted, it can be more the mounting bands, face curvature, neck length etc that can sometimes be awkward.

 

[daver2]

Welcome to VCFED as you have just joined - and the PET community.

Are you in the UK?

Shame about the CRT though.

I am not sure why you turned it on in that state though...

Dave

 

[Hugo Holden]

When there is air in the CRT, the EHT will always arc over in the gun structure. The Internal conductive coating is connect to the final anode on the gun, which is only a small distance away for the 1st anode connection, focus electrode, control grid etc. Usually, unless left like that for too long, the pcb survives but sometimes it can destroy a component like the video output transistor or the EHT rectifier.

The name for the small projecting tube, on the base, between the base pins, is called the Exhaust Tip. It is a tube that was once a long stem, that was used to evacuate the CRT at the factory, it is a vulnerable part of the CRT glass work. It is also not uncommon , if a VDU gets dropped , for the entire neck to snap off the bulb too, because of the mass of the yoke.

You will also notice, if you see a lot of dropped VDU's where the glass has cracked, neck or exhaust tip broken off, the whole VDU is not showered inside with multiple glass fragments as if the whole CRT has exploded or imploded as mainly the urban myths report that CRT's can do. More modern TV style CRT's don't tend to do this. The riskier ones for implosion antics are the early types and scope tubes with thin walled Pyrex style glass, not the TV/VDU type ones which are made of soda glass, and the bulb part and faceplate is extremely strong. If you drop a CRT off a 2nd floor balcony and it misses the swimming pool and hits concrete, you can get them to shatter that way, but even the Rock & Rollers struggled to get that to happen.

Still, if you are working with them, never let anything metal touch the glass or scratch or strike the glass anywhere, never put them directly on hard surfaces , use a soft layer of cloth or rubber. Never posture them with the neck and the bulb stilling on the surface, put them face down on a soft surface. Always use plastic tools and avoid dropping them on the floor. And you can wear protective eyewear like Polycarbonate safety glasses.

 

[gr8bit]

Hi guys,

Thanks for the replies - yes I am in the UK, and unfortunately there aren't as many old tubes available here, it seems. I think this would be easier if I lived in the states.

Hugo - thanks for the offer, but I can't send you a PM as I am a newbie. I think the cost of sending a tube from Aus -> UK might be prohibitively expensive and with quite a bit of risk attached.

I'll keep scouring eBay and a few other places to see if I can find a replacement tube. I know of one "old school" TV repair man who I will ask to see if he can find a replacement. The eBay seller has agreed to refund me if I send the PET back to him, but I would have to pay a lot more currently for a fully working PET, so it's tempting to keep it and try to repair it.

 

[daver2]

See if you can get a partial refund from the seller. It was either his/her fault for not packing it properly or the delivery companies fault.

Try both. Try eBay as well.

Did you pay by credit card? If so, try them...

You can't be expected to pay full price for something that you are now trying to fix at your expense because of a fault of a third party.

Dave

 

[Hugo Holden]

See if you can get a partial refund from the seller. It was either his/her fault for not packing it properly or the delivery companies fault.

Try both. Try eBay as well.

Did you pay by credit card? If so, try them...

You can't be expected to pay full price for something that you are now trying to fix at your expense because of a fault of a third party.

Dave

This is one reason it pays to buy things by Paypal when using ebay. Paypal do actually respond to questions quickly for help and sort these things out quite quickly.

@gr8bit:

The shipping would be the least of your worries, to get these CRT's NOS, I had to pay $400 USD each for them, and to get them here in one piece on my doorstep in a shipping container that looked like it housed an Egyptian Sarcophagus, lined with cotton wool, cost many $100's. I had to specify elaborate packing so they would not get broken in transit.

To understand why things get broken in transit, you need to watch this courier delivery scene from PET Detective (ironic isn't it ?)

 

[daver2]

I had a new works phone delivered. It arrived packed very well from the supplier and I had to personally sign for it on arrival.

My colleague bought himself a brand new iPhone. It was delivered by a courier who apparently threw it from the road to his front door. It was just lying in the drive, in the rain.

Go figure!

Dave

 

[Hugo Holden]

I had a new works phone delivered. It arrived packed very well from the supplier and I had to personally sign for it on arrival.

My colleague bought himself a brand new iPhone. It was delivered by a courier who apparently threw it from the road to his front door. It was just lying in the drive, in the rain.

Go figure!

Dave

The courier must have watched PET Detective !

 

[powerlot]

Couldn't you try to fit a 9" CRT from a compact Macintosh? I think the only issue would be the position of the mounting tabs, no?

 

[cjs]

Couldn't you try to fit a 9" CRT from a compact Macintosh?

The standard Mac monitor uses completely different sync frequencies from the standard ~15.75 kHz horizontal / 60 Hz vertical that the PET uses. In this case, you'd probably be replacing the analogue circuits that drive the tube, except for perhaps the yoke, with those from the PET, but it's not clear to me that would work. I'd be curious to hear thoughts on this from those more knowledgeable than me about this.

 

[daver2]

All we are talking about is transplanting the CRT into the PET - no electronics:

As a result, all we need to ensure are:

1. The CRT connector pinout on the rear of the tube is compatible.
2. The EHT voltage is compatible.
3. The CRT neck diameter is compatible (should we need to transplant the deflection coils).
4. The physical mountings are compatible (or can be adapted).

Dave

 

[Hugo Holden]

In these sized CRT's, the yokes are interchangeable for a fit and when the deflection angle matches, the guns are generally compatible and the heater run usually from the 12V supply. The wiring at the tube base is often but not always the same, that can be altered. And the size of the tube determines the required EHT, so that is also ok. But it pays to check the base diagram. Some CRT gun types required higher focus voltage than others, this option was generally limited in the 9" VDU without circuit mods.

The main things are the neck on the replacement is not too long, in the PET VDU, the socket is fairly close to the rear panel. The other thing is the front faceplate curvature and radius of curvature of the corners, it helps if they are a match or the front escutcheon won't fit properly. And there are the mounting ears/mounting band. These can be modified, but there are some issues, drilling/filing them is a very bad idea as it transmits high frequency vibrations into the CRT which can damage it. So it is better not to have to do that and make mechanical adapters for those instead, that is if they are not already in a position where they prevent proper mounting. The band and ears can be removed on the smaller CRT's, it is more of a mounting band than anything to do with implosion protection, but there is a trick to do it..

 

[gr8bit]

Thanks for the advice, everyone. I have bought the M24-306W/P, and it is on its way (have advised the seller to overdose on bubblewrap). I will let you know how it goes, but physically at least, it will fit - I've checked all the measurements.

Talking to someone else over the weekend, they believe that a variety of tubes were spec'd for the PET - including Sanyo and Sony, as well as the Amperex/Philips, so the board electronics are kinda.. generic? and should work with other 9" tubes. Here's hoping the -306 will just be a plug-in replacement.

Another possible option may be a Philips Cube TV (9 TC 2100) as i understand they have 9VATP4 tubes in them, which are similar to the 9VALP4 tubes found in early PETs. I am unsure at the moment whether a later control board (meant for the Amperex M24-302) would drive an earlier 9VALP4 tube, or an equivalent. But also according to this: https://www.worldradiohistory.com/BOOKSHELF-ARH/Tube-Substitution-Handbook-Radio-Shack-1980.pdf there is a difference in the voltage Eg2: ALP has 130v, whereas ATP has 90v. Both have 11v filament voltage. I confess I don't know exactly what that would mean, but it's a difference...

Another curious find related to 9VALP4 vs 9VATP4: https://console5.com/store/commodore-pet-2001-9-monitor-cap-kit-9vatp4-model-1200.html - this is a capacitor pack for a PET, but says: "The PCB itself may not have any markings but the tube will have a sticker saying 9VATP4" - this is different from other sources that have said the tube in a PET 2001 is a 9VALP4.

 

[Hugo Holden]

The 9VALP4 and the Amperex M24-302GH (and M24-302W) are in fact a little different, even though Commodore used both in the same VDU with no circuit changes. It caused a problem though, in that many of the VSU's with the Aperex tube, there is not enough negative grid bias available from the brightness POT to extinguish the beam and even on min setting it can be too bright, it was a difference in the cutoff voltage of the two guns.

The 9VALP4 was a domestic TV CRT, but the Amperex M24 parts are industrial CRT's, these are often characterized by larger heater-cathode assemblies and precision manufacturing, small focused spot size suited to computer graphics, generally they have a very long life. Many of the PET 9" Amperex CRT's are still working very well.

It is dead easy to modify CRT's circuits though and fix the brightness control issue, I explained how to do it in this article (pg 14) along with some other VDU mods to improve the 9" VDU:

www.worldphaco.com/uploads/RESTORING%20THE%20%20PET%20COMPUTER%209.pdf

All of your cited CRT's will work, the question is whether some tweaking will be required on either the focus voltage, grid bias for brightness , A1 voltage or perhaps nothing at all. These things are very easy. The main issues are the mechanical fit.

 

[gr8bit]

'New' tube arrived today, and physically the fit is just fine. New tube on left, old broken one on right (Sorry, CPC464 wanted to be in the shot)



The 7 pin neck connector will fit ok, but now the main query is the connections to the windings / coils. As you can see from the pic above, there is a difference to how these are arranged.

With the old tube (right), the yellow and blue wires seem to go to the coils towards the bottom of the screen, and the red/green to the top coils. In the new tube, the middle two connectors/wires seem to go to both top and bottom coils. So I am not sure how to wire the new tube connections to the old tube's control board.

Any pointers here would be appreciated!

 

[Gary C]

Hi

It was nice to meet you at the Museum the other day

It is possible you can reuse the yoke from the old monitor. Being a monochrome, there are no dots to need to aim specifically at so it will almost certainly work fine and it would mean the coils inductance is correct for the board already. I did this with an apple iiGS monitor. With the original yoke, the flyback wouldn't run but with the original yoke it worked fine, apart from the bloom of psychedelic colours, with a monochrome you haven't got that problem

Be careful if removing not to snap off the new tubes neck. The glue will need careful cracking off.

 

[Hutch]

It's tricky to find the right tube that's compatible electrically and mechanically for mounting.

FWIW, There has been one success sourcing replacement parts from an old Zenith TV.
This was for an older Chicklet PET with the white phosphor screen though.

Link: <https://www.facebook.com/groups/214556078753960/posts/2183853851824163/>
Tim pulled a tube and flyback transformer from a Zenith BT092Y
The tube is a 9vatp4 or 9vasp4 which could be found in other TVs.

 

[Hugo Holden]

The yoke on your donor tube is likely unsuitable, the inductances are specific to the particular circuit, and specifically the operating voltage. All you do is use your original yoke,

When you tighten the clamp up on it, after you have rotated it so the raster scan is not tilted, only do the clamp up enough to stop is rotating with mild to firm pressure. Where the plastic part of the yoke body, with the clamp around it, the glass neck surface interfaces, it pays to have some fiberglass tape, (I use Scotch 27 tape for this) at least one turn around the neck, so that the clamp area sinks into it a little and it stops the yoke body from rotating with minimal clamp force. If it is plastic directly onto glass it is more slippery, the clamp then has to be very tight to restrain the yoke without the fiberglass tape.

Notice that there is some aged tape on your old tube neck under the clamp, but not the new one. To free the old yoke initially completely remove the metal clamp. Very gently (so as not yo break the yoke plastic) on each of the plastic fingers under where the clamp was, bend them out just enough to separate them from the tape surface, they often can be stuck there embedded in the tape surface.

(presumably your CRT came from Newtubes in Canada ? they supply many CRT's with yokes on them)

 

[gr8bit]

Hi Gary, good to meet you again the other day, and I'll be back at least this weekend to return Mickey (Mouse).

I wasn't sure if the yokes were going to come off either tube successfully, which is why I was asking about the wiring. But then I took an enormous brave pill... The yokes came off quite easily. I swapped them around, put everything back in the case (secured loosely for now) and turned it on...


...


Nothing. Didn't sound like it had come on at all. No output.


...


But then I noticed the back of the tube was glowing as it should, and decided to fiddle with the brightness control. Turned it up, and SUCCESS - We have a picture!



My phone would have you believe that the text is blue and blurry, but in reality it's nearly white and crisp. Very happy with the results so far. The keyboard isn't working though, so that needs some cleaning / restoration of the rubber contacts, but that will be a walk in the park compared to this job. Then I can try setting up some test patterns to check edges, raster linearity, etc.

This is the Philips M24-306W tube. It came from an eBay seller in the UK (which is where I am). It was a new, unused "old stock" replacement tube - still in its polystyrene packaging! And with a chassis and a control board. This is the original advert: https://www.ebay.co.uk/itm/325890789334