I have started the restoration of a Heathkit SB-101, SB610, SB-600/HP-23B. I have replaced all the electrolytic caps, and have the HP-23 working well. The SB-610 is up and running and showing a good trace. I have gone through the alignment procedure for the SB-101 and get a couple steps into the Transmiter alignment and have no real transmit power out (maybe 2 watts) showing on the dummy load meter and oscilloscope.
I ran all the tubes except the AO2 (it seems to be operating well in circuit) across my Sencor tube tester and they all pass that test with flying colors. I know that is not a true test but it shows tube function. I have 820 VDC on the 6146B tube plates, -6.4 VDC on pin 3 unkeyed and 242 VDC keyed, pins 1,4 and 6 are right at 0 and pin 5 is at -63 unkeyed and flop to modulated negative voltage when keyed.
Also there are 3 small coax “break out“ RCA cables coming out of the back of the radio labled A, I and O. I can only theoretically think that they were taps for the SB-610 and/or to key an amplifier. The SB-610, SB-101 and SB-600/HP-23 were purchased as a set from a SK. The SB-610 came with it’s manual but there are no clues inside about the 3 RCA cables.
A is tapped to relay socket BG. Oops like pin 7 but it is hard to tell.
I is a tap from V2 on the modulator board looks to be pin 5.
O is a tap from one of the ceramic disc caps adjacent to V2 on the same board.
The receiver alignment is good and the radio sounds fantastic as I tune around the bands. I just need to find the derailment of the transmit power.
The mic I am using is a ElectroVoice 638 and I have also tried an old white Heathkit hand mic.
ths is my first tube radio project. I have rebuilt/repaired a couple of RF amplifiers one of which is the SB-220 I will run with this. I have also repaired more than a few tube guitar amplifiers in my day. So I shouldn’t be a complete idiot. I just need a little help with this radio thing.
Thank you in advance for any guidance you have.
Dave KO4HRT
I ran all the tubes except the AO2 (it seems to be operating well in circuit) across my Sencor tube tester and they all pass that test with flying colors. I know that is not a true test but it shows tube function. I have 820 VDC on the 6146B tube plates, -6.4 VDC on pin 3 unkeyed and 242 VDC keyed, pins 1,4 and 6 are right at 0 and pin 5 is at -63 unkeyed and flop to modulated negative voltage when keyed.
Also there are 3 small coax “break out“ RCA cables coming out of the back of the radio labled A, I and O. I can only theoretically think that they were taps for the SB-610 and/or to key an amplifier. The SB-610, SB-101 and SB-600/HP-23 were purchased as a set from a SK. The SB-610 came with it’s manual but there are no clues inside about the 3 RCA cables.
A is tapped to relay socket BG. Oops like pin 7 but it is hard to tell.
I is a tap from V2 on the modulator board looks to be pin 5.
O is a tap from one of the ceramic disc caps adjacent to V2 on the same board.
The receiver alignment is good and the radio sounds fantastic as I tune around the bands. I just need to find the derailment of the transmit power.
The mic I am using is a ElectroVoice 638 and I have also tried an old white Heathkit hand mic.
ths is my first tube radio project. I have rebuilt/repaired a couple of RF amplifiers one of which is the SB-220 I will run with this. I have also repaired more than a few tube guitar amplifiers in my day. So I shouldn’t be a complete idiot. I just need a little help with this radio thing.
Thank you in advance for any guidance you have.
Dave KO4HRT
