The Hallicrafters SX-130
Written by Bryce Ringwood   
The Hallicrafters SX-130 was made from 1965 to 1969. It is a single conversion superhet covering 0.56 to 31.5 MHz in 4 bands. It is a single superhet with an intermediate frequency (I.F.) of 1650kHz. The S-129 is the same set minus crystal filter.
 
The bands covered are: .535-1.61, 1.725-4.7, 4.5-13 and 11.9-31.5 MHz.
 
Measured sensitivity was better than 1uV on all bands.
 
Reception modes are AM, CW and SSB. 
 
The set uses the following valves
 
6DC6 - RF amplifier
6EA8 - Local oscillator /mixer
6EA8 - IF amp/BFO
6BA6 (EF93) - IF |Amp
6BE6 - Product detector
6AL5 - Detector/NL
6GW8 (ECL86) - 1st and 2nd Audio
 
The set uses a single silicon diode in a half-wave power supply. That isn't very nice,(actually, it is horrible) but it works.
Hallicrafters SX-130 and Custom Speaker
 
SX-130 and Custom Speaker

Controls

 
B.F.O Pitch, Reception Mode, Crystal Phasing, Volume, Sensitivity, Main Tuning, Bandspread, BFO ON/OFF,Antenna Tuning, ANL ON/OFF, Receive/Standby, Phones. The set has an 'S' Meter calibrated 0-9 and db.
 
The main tuning dial lamp on the set was too bright for the owner, who wanted it to be dimmable. He also complained the set had dropped off in sensitivity. After correcting the speaker wiring, there seemed to nothing wrong with the sensitivity. I think the problem may have been that the broadcasting station operating on medium wave seems to very in signal strength quite markedly. 
 

About this set

 
There is a problem with this particular set - it crackles. The level of the crackles is quite small now - they are drowned out by antenna noise. It would seem they originate in the primary of the first IF transformer. Removing the first 6EA8 does not remove the crackles. Removing the input to the 2nd 6EA8 removes the crackles. Running the set off an independent power supply does not remove the crackles. I suspect the purpose-made tuning caps inside the IF transformers. These look like a layer of plates sitting on the bottom of the transformer.
 
Crackling and frying noises are caused by small electrical discharges. Usually they are associated with carbon resistors, but any breakdown in insulation can cause random discharges.
 
In this case the crackling became more severe as the HT voltage was increased. I managed to reduce the problem somewhat by replacing the resistor in the anode circuit with a modern carbon film type -but I could not eliminate it entirely.
 
The IF transformers resemble very large transistor types in construction. They have huge ferrite pots covering the windings. These run in an external thread. I assume the capacitors built into the frame are mica. There is an odd metal link that I assume is used for coupling. It is far from obvious what is causing the discharge producing the crackling
 
Each front end coil has a tunable ferrite core and trim capacitor, facilitating accurate tracking adjustment.
 

In use

 
The set is sensitive and very easy to use. It has an antenna trimmer to get the maximum RF performance.
 
The dial lamp on the main tuning scale was too bright for me also. It really does need a dimmer (much as I hate modifying sets). The dimmer mod works really well. Alas, the scale markings are small and difficult to read, dimmer or no dimmer.
 
The tuning mechanism is via dial cord (but no complicated parallel pointer stringing as per the SX-71). The bandspread dial has to be set to 100 for correct calibration of the main dial. As I do the SX-71, I slightly move the bandspread dial in from its calibration point to make fine-tuning easier. The only reason I didn't hear any DX (ham speak for long - distance reception) was because I was so busy listening to it on the SX-71. I'm sure this set is just as good in this respect.
 
Sound quality is good through the 4" oak cabinet bookcase speaker I made (well, sort of designed - my woodworking skills are deplorable) for the owner. I think I will organise one for myself. Maybe two.
 
All in all it is a good shortwave receiver for broadcast listening. 
 
 
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