Working on the tuner chassis of my pretty much original 38-690; I have replaced 40 paper/wax and electrolytic capacitors (restuffed), and 10 out of spec resistors. Repaired a lot of veneer and refinished the cabinet. In addition, I have rebuilt the condenser coupler, replaced the tuner bushing, and the sub chassis isolators. And the dial.....
Questions that I have are-
The band mask slot for the broadcast band does not line up; the beam lens center is on the edge of the window- is there a way to adjust it? The others are ok.....the arm on the band switch is pot metal, so cannot be bent, and the arc shaped link can’t be adjusted.
The band knob (repro) swings from horizontal to vertical; is that correct?
The pointers on the 4 other knobs do not seem to point in logical directions ( not from 7 o’clock to 5 o’clock)- normal? All 4 knobs are the same part from what I can tell; two of the shafts are flatted on opposite sides, but installed either way, the pointer doesn’t swing symmetrically.
It was disassembled when I found it.
Welcome to the Phorum!
sorry, I haven't worked on a 38-690 so others will have to help out.
Probably answered my own questions; Google images show the band switch knob swinging to the left, as mine does. The Bass pointer lines up with “off”, and the Magnetic Tuning knob lines up- the other two are the ones that puzzle me.
Trust that I have read them all multiple times (sometimes after learning the same myself before reading). I powered up the dial illumination and the beam indicator on the broadcast band isn’t too bad, so I will leave it. Now, on to the power chassis, which will be comparatively easy.....
Well...the power chassis is a mess. The interstage transformer has an open primary, one choke is open, and the AVC 6J5 is broken. Theory that I have is the filter cap shorted, which caused excessive current through the choke, which burned out. This is on the side with the candohm voltage divider resistors; if the choke goes open, no current flows, which means no bias voltage source. As the 6F6 driver is fixed bias and fed from the other power transformer, no bias caused excessive plate current, which burned out the interstage primary winding. Oh, well.....
I read somewhere that Heyboer is now out of business.
Their website is still up:
https://www.heyboertransformers.com/
I would contact them and confirm they are still rewinding transformers before proceeding.
Hello Ron,
I see they have a up to date Facebook page with a Christmas photo !
Sincerely richard
Well, it could very well be that what I read was fake news. I hope Heyboer is still around, they do great work.
Well, the cost to rewind the interstage transformer and a new filter choke isn’t in the cards for now, so I came up with a temporary (maybe permanent) solution-
As 4 of the 6 filter caps on the power supply were not original, I restuffed the 2 originals and replaced one of the others with a multi section cap, along with a discrete axial cap- this got the power supply handled and left 3 can cap holes, 2 of which I filled with dead caps (leads clipped) for visual purposes.
I then made an adapter to install another octal socket were the last cap was. I fully disconnected the interstage transformer and bundled the leads out of the way, in case I decide to have it rewound. I wired the additional octal for a 6SN7 split load phase inverter, with a DC coupled driver. I installed a single ended output transformer on the 6F6 to drive the tweeters.
Now I have a functional on all bands 38-690, with no permanent modifications.
Good work around. The radio works on all bands an in the future could always be returned to original build. David
Getting ready to perform the RF alignment on my 38-690, and I have a question- the broadcast band works/ receives fairly well, but the dial is off by 40kc. Mechanically, the dial stops line up with the scale ends. Any tips, or will the standard process correct this?
Well, either you turn the dial itself (forgot if this could be done; there is a notch on the inner ring) or this is what the alignment is for: you simply adjust your padders.
