EICO HFT-90 Tuner Problem

11/29/2010 7:26:27 PMLeslie

Hello All,
I have an EICO HFT-90 which is a sweet little FM tuner. Everything works as it should (sweet vacuum tube sound, selectivity, sensitivity). The only problem is the illuminated dial pointer (a DM70 tube with an exclamation mark on it).

The way it is supposed to function, is that as one tunes onto a strong station, the exclamation point enlarges a bit and becomes brighter than it is between stations--a variation on the 'tuning eye'.

In this case the tube light works in reverse; it becomes brighter between stations and the shaft of the exclamation point becomes dimmer when one tunes in a signal. I realize these were kits, and someone may have soldered something in backwards, though I can't find the problem yet.

I have checked the resistors in the circuit relating to the 4 wires from the DM70 socket, and replaced the 10uf/25V electrolytic capacitor (C13 in the HFT-90 manual)that the socket wires run into on the chassis circuit.

i've no way of testing the tube, and am unsure whether replacing it would solve the problem.

Any advice greatly appreciated, as I'd like the rig to be 100% (or as close as possible).

Cheers,

Leslie

11/29/2010 8:47:33 PMWarren

I think you made an error in that it is working as it should. The manual says " Correct Tuning is indicated by Maximum Contraction of the tuning eye "

Download the manual here

http://www.schematicsunlimited.com/?z=eico

11/29/2010 10:32:01 PMEdd

Sir Leslie. . . . .

Had poked this up earlier . . . and see that Sir Warren has come back and is also in like concurrance . . . so I am still posting additionally.

The DM-70 traveling tuning eye travels along the slide rule dial as a luminous "exclamation point" indicator, contracting as the exact center of each broadcast channel is tuned in to.

If you have this as a new acquisition, and are not full familiar with it, sounds like it is acting just EXACTLY as it should.

It is detecting the "zero" null as a FM station is preee--cisely tuned into , nose on.

No problem with the tube if it is responding as above.

73's de Edd

:I think you made an error in that it is working as it should. The manual says " Correct Tuning is indicated by Maximum Contraction of the tuning eye "
:
:Download the manual here
:

:http://www.schematicsunlimited.com/?z=eico
:
:

11/29/2010 11:37:58 PMLeslie

:I think you made an error in that it is working as it should. The manual says " Correct Tuning is indicated by Maximum Contraction of the tuning eye "
:
:Download the manual here
:
:http://www.schematicsunlimited.com/?z=eico

Dear Warren and Edd,

Silly old me, red-faced. Thanks for that (saves me being driven crazy); I guess I made an unwarranted leap about correct function based on the fact that I would have had it light up when it zeroed in on the station (like the old cat's eye tuning tube).

Ah well.

Cheers, and have a great evening,

Leslie

PS: the tube is a little faint I think (based on pictures I've seen) so I might go for a replacement just to be on the safe side. My tester won't work with one of these mini-tubes.
:
:
:

11/29/2010 11:41:38 PMThomas Dermody

Regarding subminiature tubes, you can place the wires in the socket holes of your tester. However, it isn't the cathode's emission that goes bad with these cathode ray indicators, but the phosphorous. It dims with age.