Troubleshootin Hammarlund SP-600

[iw5ci]

I Got a new SP-600 from a friend and i would like to repair it. I need help as i am just learning to work on this beauties (i have recapped my 600 with good results).

About the new one is that is different from the other. For example there is no Diode output . Instead it have a PHONO input.

The capacitors are also different. Ceramic or Sprague bathtub instead of BBOD , unfortunately there insn't' the version plate as it have been removed.

Actually the radio turns on , i can ear white noise from the speaker and if insert an audio signal in the rear phono input i can ear it amplified in the speaker. So the BF section is operational, but the radio doesn't receive anything. No signals in any band even if i insert a strong signal with the generator in the antenna plug.

i have cheched the RF section tubes and they are good. Now i have to make some test to insulate where is located the fault before starting to change components without reason . Where to start from?

I have a digital tester a signal generator and a station monitor that i can use as oscilloscope anything else.

thanks for help!

[SM6OID]

Hej !

I've been told that SP-600's above serialnumber "17 000 something" do not have the Black Beautys of Sudden Death, ceramic caps are used instead. Both my SP-600 JX-21 are slightly above serialnumber 20 000, hence I do not have a problem with the capacitors. BUT I do have "Diode load output" not "phono".

Next simple step can be to inject IF to see if that part is alive, and I would guess it is since you hear noice?
What does the S-meter tell you?

[iw5ci]

The S-meter does not show any movement. The coil in not open (of course)

i can ear a change of wideness in the white noise if i switch between the different bandwidth of the receiver, how do i inject a  signal in the iF? with the signal generator?
exactly where i have to inject and at which frequency?

[WQ9E]

Which model of SP-600 do you have?  It it has the crystal controlled first oscillator option cycle this switch a few times since corrosion here will cause the first (HFO) oscillator not to work.  If this doesn't help, with your symptoms the first thing I would check is whether the HFO is operating.  On the lower ranges the first oscillator operates at 455 Khz higher than the dial frequency.  So put a test receiver (preferably with a BFO) near your SP-600 and run a short wire from the test receiver's antenna input near V-4.  Tune the test receiver to 1.455 Mhz and then tune the SP-600 a small distance either side of 1.000 Mhz.  If the HFO is working  you will hear a signal from it in your test receiver.

If it isn't the HFO, then start by injecting a 455 Khz signal into the grid of V-9.  If this IF is working, pay close attention to the switching system used to change the SP-600 from single to dual conversion depending upon the range.

[iw5ci]

Fortunately after washing the sp-600 , cooking it in the oven for a night at 50 celsius and then cleaning the tube sockets , and all moving contacts the radio came into life and worked perfectly (with very good stability and sensibility) for a couple of hours.
Then it developed a new problem: agc is no more working. i have full scale deflection of the s-meter on the signals and distorted audio even if i put rf-gain to zero in avc mode on. If i switch to manual gain the radio works ok.
When in avc, even if i advance the volume control just slightly from zero position i have a lot of audio gain and distortion.
The radio settled for 25 years in a "barn".
I don't' know exacly the version because it have been demilitarized, maybe from a NATO command here in italy (as i found in the rf turret a piece of tape written in italian "checked in may 1968") and the version plate has been removed.
I post some photos..

[iw5ci]

you cannot see in the photos, but many capacitor have been changed to ceramic even if there are still some gray sprague old type capacitors (maybe they are better than the black bbod?!) the capacitor upgrade have been done almost 25 years ago because in the last 25 years the radio was settled in a barn.

which component can affect the working of avc and cause the problem exposed?

[WQ9E]

A leaky bypass cap on the AGC line would be my prime suspect and some of those will be in the turret assembly.  A gassy tube can also cause this symptom but in the SP-600 I am afraid you are in for some more recapping work.

If you want to narrow it down you could isolate (by disconnecting) parts of the AGC bus but if it still has suspect capacitors your time is going to be better spent replacing them all in this radio. 

[w3jn]

In addition to Rodger's advice, you might want to zero in on any oil tub capacitors in the AVC circuit.  Although in general they last a long time, I had a dual-section oil tub leak from section to section in a 51J-4.  1/2 was in the AVC circuit and the other half had some 50VDC on it from somewhere - the leak ended up putting about 5 volts positive on the AVC bus.

You might also have a bad AVC rectifier tube.  Rare, but it happens.

[iw5ci]

Yesss. It was a shorted capacitor in the AVC bus. One of the color banded gray sprague capacitor. I decided to completely recap all sprague capacitors (RF DRUM, RF deck and under chassis). Now the job is done and the AVG works great.
Anyway the sensibility of the radio is not optimal.
There is a neat decrease of signal level when i switch from 8 to 3 khz bandwidth and in any selectivity position the sensibility is not the one aspected.
My other sp-600 is definitely more sensible.
I have realigned the rf deck , checked tubes etc.. but i suppose there is still something wrong ... some suggestions?

[WQ9E]

Did you align the IF in addition to the RF deck?  This sounds like an issue with the IF because the sensitivity is changing considerably when you reduce the bandwidth.  Do any of the IF transformers show a broad, shallow peak because that could indicate a transformer with a bad capacitor inside.

[iw5ci]

well i have no instruments except signal generator and smeter reading.
Is it possible to align the if deck anyway and how?

What i have noted realigning the rf deck is that i have a narrow peak (in all bands) when i align the variable condensers of the upper segment of the bands, while when i move the variable consenser for the low part of the band i have a broad response without a neat peak. Is it normal or it is a problem?

[WQ9E]

Your RF alignment sounds normal, the inductance alignment at the low end sounds normal since these are multi-turn adjustments.

Although Hammarlund calls for a sweep generator for the SP-600 you can do a pretty good job by setting your signal generator for the crystal frequency and then aligning using the S meter.

[iw5ci]

so i must set the generator to 455 khz and then peak the coil turrets for maximum peak with the bandwidth set at the maximum selectivity and phase shift in the middle of the course?

[WQ9E]

You will set the generator close to 455, the actual frequency would be centered on the single crystal filter which may not be on exactly 455 Khz.  Once there I would do the alignment with the SP-600 set for 3Khz. Non-XTAL selectivity.  Keep your signal generator output fairly low, just enough to have a reasonable reading on the S meter.