In at the deep end with a Pam 30

[Farzooks]

I haven't touched a valve set in a long time, so bought one that doesn't work to get my hand back in.
I've no doubt trials and tribulations await...

[Cobaltblue]

Hi Farzooks

Is this a PAM TR30 like the one in this thread ?
https://www.vintage-radio.net/forum/...ad.php?t=99142

Cheers

Mike T

[Farzooks]

Yep, same as that one, but shabbier

[Boater Sam]

Can you safely work on a chassis that is connected to one side of the mains - without a transformer?

[Herald1360]

Yes with chassis neutral and the same degree of care as used for working on any set with high voltages around.

Or was that a specific question directed at Farzooks?

[Boater Sam]

I was asking Farzooks, but its a fair question to ask of anyone who has not demonstrated their competence or experience of working in contact with the mains I think.

[Graham G3ZVT]

Originally Posted by Boater Sam

Can you safely work on a chassis that is connected to one side of the mains - without a transformer?

Depends on how safe is "safe".
When I started with Granada TV Rental in 1971 all the bench positions were equipped with an isolation transformer, but those of us in the field were expected to manage without them in the customers premises. We were issued with a neon screwdriver to check that the chassis was neutral (such an instrument would be forbidden by modern H&S).

You couldn't assume that the power socket the set was plugged into had the correct "polarity" (L&N), it was not uncommon to find it reversed, especially was one of the old pre-BS1363 types we encountered, (eg 5A or 15A round pin, Wylex). Remember that in the case of a fused plug, with reversed L&N (D&S or a modern 13A), the fuse will effectively be bypassed in the case of a L to E short so you are at the mercy of the 30A fuse wire in the CU which may just possibly be a six inch nail.

We eventually were issued with a torrential handbag-shaped transformer, but it was still quite a heavy thing to carry up flights of stairs and I don't recall it being a misconduct issue if we chose not to use it.

Later on, some colour sets used a bridge rectifier and the chassis was connected to the -ve so it was live regardless of mains "polarity", but as far as I know, no domestic valve radio set used that arrangement so i'll stop there...

Graham.
G3ZVT

[Alistair D]

I agree with the above comments about safe working practices and the fact that an isolation transformer is not necessary. The exception is that if you intend to connect an earthed instrument to the set then it must be fed from an isolation transformer.

Al

[Argus25]

There can be some other issues if you do not use an isolating transformer on a " Power Transformer-less" radio or TV chassis that is neutral connected:

Practically all GPO (general purpose outlets) now are protected by RCD's. In the neutral connected chassis set, at least one safety advantage is that the breaker box RCD still provides electric shock protection for earth currents. If one point in the circuitry with a high enough potential is touched by a person, or an earthed test instrument, there will be protection to an unbalanced current and the RCD will trip. So from a safety perspective alone that might be favorable, but there is more to consider........

Likely the GPO will be one of a few in the workshop area connected to the same RCD, so very quickly you will end up taking out the power to the whole workshop when the RCD trips as you end up touching something in the sets circuitry, or connecting other test gear to it which might have some earth leakage. This is really inconvenient, especially as workshop computers, test gear, clocks etc lose power and need to be reset.

To avoid this I always use an isolating transformer on the hot chassis sets, it avoids these inconveniences, and deals with the possibility of a reversed phase & neutral connection in the plug. The isolating transformer isolates the breaker box RCD. It also makes it safer to connect earthed test gear and reduces the chance of knocking out the workshop power. It just pays to remember that the isolating transformer has defeated the breaker box RCD.

[Boater Sam]

All worthy comments. I did not intend to highjack the thread onto Isolating transformers, but merely to find out if the OP was confident and competent to work safely.
This subject has been aired often on the forum.

[Farzooks]

Yes, I learned that lesson a long time ago when a bench lamp touched a live chassis. There was an interesting spark.

[ukcol]

Although general advice about working on live chassis sets is a good thing to offer to a beginner, it is worth pointing out (in order not to confuse Farzooks) that the PAM TR30 is NOT a live chassis set.

[Farzooks]

https://www.vintage-radio.net/forum/...d.php?t=139950

Can't believe I bought this a year ago. It's been sitting on top of the washing machine, nagging at me every time I pass it.

Anyway, a start of sorts. I took the back off and made sure all the valve sockets were populated, as the seller had said something to the effect that 'valves were missing or gone'. Whether he was simply repeating what he'd been told or picked it up wrong, I don't know, but they were all there. Whether they're all the right valves in the right places, I don't know yet - data sheet will be on order soon.
I ran the set up gradually on a lamp dimmer, just briefly so as to avoid stressing things that hadn't seen any mains voltage for a few years, in all probability. Did that a few times, and eventually plugged it straight into the wall. I had been gratified to see all the valves in my field of view lighting up, and both dial lamps chimed in, one albeit a bit reluctantly.
Because the tuning cord was broken, I had to manually position the tuning cap, between plug-in sessions, as I wasn't sticking my hand into an unknown chassis quite yet. Eventually I was rewarded with a Spanish football match on MW, but nothing on LW or VHF yet.
There was a fair old bit of mains hum at one point but that's mostly disappeared as things settled down. There's a fearsome crackling from the volume pot and the wavechange keys, but I'm not terribly surprised at this. Whether that's also a symptom of a deeper malaise I've yet to find out.

I rather like this set already; it seems well built, and the three speakers hold out some promise of a decent sound.
The discovery of the link of this set to the VHF2D is handy, as there's almost nothing relating to either this set or its alter-ego the Invicta 40

[Boater Sam]

Read the stickies! Note replacing "that" capacitor before you run it ! Sam.

[Farzooks]

Originally Posted by Boater Sam

Read the stickies! Note replacing "that" capacitor before you run it ! Sam.

That's the first thing to do once I get the cabinet off, agreed.

[Freya]

When we as a forum refer to "That Capacitor" to newer users, surely it should be also given its correct terminology in the same sentence.
It irritates the hell out of me when it has a correct name.
Rant over