Ferguson 382U Firefly not playing ball
 

Hi,

I've been working on and off for the last 6 months on our old family radio, which has been unused for many years. I've replaced a number of caps and resistors and I think 4 out of the 6 valves.

I now have Audio amplification at last, but nothing as far as AM or FM :(

I know my heaters are now all working and I've had a scope on the IF stages and can see nothing.

One thing that still puzzles me is what appears to be the VERY high HT on the anode of my "V2" A (463V) and B (231V) on a UCH81, with zero volts on the Grid, according to my 500V standard DVM

Does anyone know what could be causing this at all?

Any suggestions welcomed!

Re: Fergusonb 382U Firefly not playing ball
 

Worthwhile confirming your DVM is working correctly, the DC voltage from the UY85 is only 252v.

Re: Ferguson 382U Firefly not playing ball
 

B is the mixer anode and is about right. A is the oscillator anode so either you have the decimal point missing or your meter is not happy with the RF.

I suggest you start with MW and try measuring the voltages again. Pin 9 is the oscillator grid and should be -ve if oscillating. Pin 8 is the oscillator anode (your A) and if it is much lower than the trader value then the oscillator is not running.

Re: Ferguson 382U Firefly not playing ball
 

Have you checked the voltages on V2 with the radio switched to FM and then AM, and compared? Check C21, C23, C24. make sure wave change switches are clean.

Worth a check of voltages around UABC80.

Take a voltage readings switched to FM & AM of V2, V3, V4 and post.

Have you got a analogue meter as many of the voltages were measured with reference to AVO 8 at the time, digital meters were not common in those days.

John

Re: Ferguson 382U Firefly not playing ball
 

That is most likely the problem. Some digital meters just do not like the presence of RF and will give incorrect readings. Think about it.....you cannot possibly have more than the cathode voltage of the rectifier anywhere in the set so the reading has to be false. Try another meter or use the scope to measure the DC voltage (and it will probably also show the RF sitting on top) unless it's damping the oscillator sufficiently to stop it.

Re: Ferguson 382U Firefly not playing ball
 

Thanks guys! I've found my Italian "ICE" Microtest 80" and I'll run over these voltages now!

Re: Ferguson 382U Firefly not playing ball
 

Okay, switched to FM we have:

V2 a=0V b=159V
V3 = 201V
V4 = 97V
n.b. V6 = 248V

On MW we have:

V2 a= 166V b= 209V
V3 = 214V
V4 = 118V

I'm definitely suspicious of the wafer wave change switch too, but can't think of an easy way to circumvent it and get it out of the picture, given the multitude of contacts.. :)

Re: Ferguson 382U Firefly not playing ball
 

Your volts on FM are not far away from manufacturer reading, little high on MW, HT is spot on.

Have you checked decoupling caps C21 C23 C24? You could have a duff UCC85 giving you no FM. Check your grid 1 on V2, should be a minus voltage.

You can always have a go at cleaning wave change switch with a little switch cleaner and old tooth brush, though you should get clicks and pops when switching especially if dirty. Have you any other equipment such as signal generator, signal injector or signal tracer?

John

Re: Ferguson 382U Firefly not playing ball
 

Thanks John!

DC Resistance check on these:-

C21 - o/c
C23 - o/c
C24 has 18.5K Ohms ( replaced it and it still has 18.5K Ohms! )

Grid 1 voltage ( measured at tuner connection point no. 7 ) -0.50V

Nothing on the wave change switch - completely silent..

Re: Ferguson 382U Firefly not playing ball
 

Get MW working first so set the switch to MW and leave it there for the time being. We need to know the V2 voltages on Pin 8 (oscillator anode) Pin 9 (oscillator grid).

Have you replaced any capacitors yet? A resistance measurement will not tell you if a capacitor is working correctly nor if it is leaking as the test voltage is too low.

How do you know you have audio amplification?
What service notes are you using? Is it the trader sheet 1299?

Re: Ferguson 382U Firefly not playing ball
 

Hi PJL,

Thanks for suggestions, set to MW we have:

V2 Pin8 = 172V Pin 9 = 0V

C48 replaced
C50 replaced
C54 replaced
C51 replaced
C45 replaced
C23 replaced
C24 replaced
C16 replaced

I can feed an MP3 player output though to the "pre amp" stage of the UABC80 and I get sound.

Yes, I am using the "Trader Sheet 1299",

many thanks, Pete

Re: Ferguson 382U Firefly not playing ball
 

Sorry I have been using the Manufacturers circuit diagram so capacitors I would suspect on Trader Sheet is C22, C21 .0047uf.Have you tried another UCH81? would also replace C53 across output transformer as it could cause serious problems if it went short.
John

Re: Ferguson 382U Firefly not playing ball
 

The voltages suggest that the UCH81 is low emission, eg: Va = 172v, Vg = 0v, Ia = 1.5mA.

Lawrence.

Re: Ferguson 382U Firefly not playing ball
 

C16? are you sure as this is 33pF?

The oscillator self regulates by rectification on the grid resulting in a -ve grid voltage Yours is not showing the negative voltage but that is not conclusive as the meter probe capacitance can stop the oscillator.

The oscillator anode is showing high compared to the trader. This would imply the triode is oscillating as the -ve voltage on the grid caused by the self-regulation reduces the anode current. One alternative is the valve is low emissions so it might be worth trying your spare and measuring the anode voltage again.

As John mentions, the wavechange switch causes all sorts of problems - did you manage to clean it?

Re: Ferguson 382U Firefly not playing ball
 

Using a 1M probe tip helps. Cheap DVMs are about 1M input and better ones are 10M. The Philips Colette actually filters the DK96 (which runs on FM and Gram) to increase the negative bias on the push pull output stage.

Even a 10:1 probe on a scope may kill a VHF LO and badly pull off AM LO or IF alignment on valve IFTs.

Re: Ferguson 382U Firefly not playing ball
 

Hi - I've had another look at the Wavechange switch and the contacts I can see/clean seem to be okay. Unfortunately, as it seems very well entrenched, I'm not sure how much can be done without unsoldering all the connections, to free it up for an inspection of the contacts on the other side of the wafer..

Checking through the valves I've replaced so far we have: UABC80 ( no heater ), UF89 (swapped on spec I believe) and the UCC85 (no heater). I've now ordered a UCH81 (NOS I believe), so hopefully we can give that a try..

Pete

Re: Ferguson 382U Firefly not playing ball
 

Okay at last.. new UCH81 in place and although no fix, I do now at least get 'clicks' when I switch between wavebands..

V2 Pin8 now = 108V Pin 9 = -9V
V2 b now = 187V

Pete

Re: Ferguson 382U Firefly not playing ball
 

I struggled with a Ferguson 382U back in about 1985, the fault turned out to be one of the capacitors inside the IF can (C34 or C35). It's the only set I have ever had this problem with.

As has been suggested, a signal generator would help narrow the fault down to a particular stage. In the absence of one, it might be worth trying a 220pF temporarily at the base of the can across L14 and L15 in turn to see if this improves things.

Re: Ferguson 382U Firefly not playing ball
 

Good progress, the grid is -ve so it looks like the oscillator is running now.

Have you cleaned all of the valve pins? I always like to check the DC conditions of all the valves. Set to MW and measure the voltages on V3 grid(2), anode(7) & screen grid(8).

Re: Ferguson 382U Firefly not playing ball
 

Hi chaps.

220 pf cap - tried across L15 - got very slight crackle?

measuring V3 set to MW:

grid = 0V
anode = 196V ( was falling to around 100V and after a few mins jumped up to 196V )
sc grid = 90V

Pete