Marconi TF2700 Bridge

[pwdrive]

No I do not understand at all it can be clearly seen from the events documented in the first paragraph of my last post that the item was wrongly described both pictorially and in the written word, check out the listings yourself under completed listings, the seller must have known it was faulty unless he/she deligated the whole process to another party, I have no intention of contacting the seller :
a) Because I did not win the auction, my wife did.
b) Even if I did I would not waste my breath and my time doing so.


Also note that my temporary repair is, as has been explained, just that. When I have time to repair it properly the unit will be up to original specs. and if at any future date I did decide to sell it it's service history while in my occupation will be well documented and available to any prospective purchaser.
As to the unobtainium properties of the potentiometer I am afraid I have to disagree...what about a good second hand one from a donor unit, failing that a pot within a pot is a repair technique I have used succesfully in the past

Lawrence.

[Mark Hennessy]

Lawrence,

It's entirely up to you, and I apologise for trying to convince you otherwise. I still don't "buy" your stated reasons for not contacting the seller, and I hoped that my experiences might persuade you to at least give it a go, but as I say, it's up to you: it's your time; it's your money.

The mention of the potentiometer was an example of how you might bolster your argument with the seller; not to suggest that you aren't capable of finding ways to fix it.

However it may have seemed to you, my messages were intended to help you (and the wider eBay community). Once again, I apologise for trying, and will return to "lurk" mode.

Sincerely,

Mark

[AlanBeckett]

You've got me worried now
I'll have to go and give mine a more thorough test.
Alan

[pwdrive]

Hi Mark, no worries, when I consider what we have made on Ebay and what we have lost then basically we are quids in by a long way.
The faults that I located on the instrument are no bother in themselves and I consider them as a relatively easy fix compared to some of the repairs I have had to do over the years. As to my troubleshooting capabilities they are pretty good, I was top of my game when in the trade.
I would now request that any members don't pursue the Ebay part of this thread, I am however fully willing to discuss the merits and practical/technical side of the Marconi TF2700 bridge or on any other piece of gear.
As to Marks attempts to inform me otherwise then it is no problem he was only trying to help and I fully understand that.

Lawrence.

[pwdrive]

You've got me worried now
I'll have to go and give mine a more thorough test.
Alan

Hello Alan you shoudn't worry, when asked if I worry I always reply...No, I just think a lot.

Apparently each balance pot and it's scale were individualy paired at the factory.

Lawrence.

[Skywave]

Apparently each balance pot and it's scale were individually paired at the factory.

Lawrence.

The predecessor to the TF2700 - the TF868 - was also individually calibrated to each machine in the factory as well.

Al.

[pwdrive]

Yes, I picked up on this regarding the TF2700 from an old post on UKVRR forum, I think the gentleman concerned worked for Marconi.
How does the TF868 perform?

Lawrence

[Skywave]

TF868: performance. Well, first of all, there are several variants in existence. The original was the TF 868; I have the TF 868B. That implies that there was a TF 868A - but I've never seen one.

First, the spec.:
Inductance: 1 µH to 100 H in 7 decades; measurement at 1 kHz or 10 kHz.
Capacitance: 1 pF to 100 µF in 7 decades; measurement at 1 kHz or 10 kHz.
Resistance: 0.1 Ω to 100 MΩ in 8 decades; measurement at d.c.
Q: 0.1 to 10 at 1 kHz; 1 to 100 at 10 kHz.
tan δ: 0.001 to 0.1 at 1 kHz; 0.01 to 1 at 10 kHz

Since Q = 1/tan δ, the scales (Q and tan δ) when combined give an extended Q measurement range up to 1,000 and tan δ to 10.

Marconi also made a D.C. choke adapter for this unit, enabling the inductance of coils, chokes, etc. to be determined whilst that component was passing d.c. (useful for measuring swinging chokes, for example).

The weight of the item is 12 kg.; H = 11"; W = 19"; D = 10" (approx.)
So it's big and a bit heavy!

Performance:
Obviously I can only vouch for mine. I do own some accurately-calibrated R, L and C components: these give an accurate indication on my TF 868B ('accurate' enough for 99.9% for my purposes ).

Construction.
Internally, very sturdy. However, maintenance is not a trivial task - and that remark ignores the several specially-selected components within it.
I have an original TF 868B Marconi Operating Instructions Manual (ref. EB 868B), but the one I obtained from the 'Net (ref. OM 868B) is much better.

As soon as I can, I will take some photos. and add them to the Gallery, with an accompanying write-up.

Al.

[pwdrive]

Thanks for the run down Al, I did not realise it had two test frequencies, the TF2700 only having one internally (1Khz) although it will take up to 20 Khz from an external source as well as ext DC input for chokes and electrolytics.
By the way a Marconi Q meter and matching generator have just been listed, collect only so that's me out. The TF2700 is very easy to get at internally.

Lawrence

[Skywave]

TF 868B: two test freqs. The reason for two is that certain reactive components can have reactance-to-resistance ratios or opposite phase reactances which at 1 kHz (normal test freq.), unwanted side-effects - such as resonance, or a near resonance condition - can give rise to errors of measurement. For such cases, 10 kHz is used.
The bridge also features a "R x 10" switch, for measuring very high values of resistance.

I'll have a look at those items you mentioned; thanks.

Al.