all pix in this section are "as received"
Initial observations are that this is one of the nicest R-388's I've seen. The front panel seems very clean, as is the chassis, with the exception of an area near the power transformer. It does have the 3 bristol wrenches, and the angle screwdriver, which I've never seen in one before, but it does not have the alignment tools that fit inside the rt side panel. The bristol wrenches are mounted inside the top cover, & the screwdriver on the outside. The inside of the top cover has the usual very readable schematic attached, with a hand done note on a small mod. to the break-in ckt. Once the knobs were removed, and cleaning of the panel started, it became obvious that there was a substantial amount of dirt on it. Pictures below will show that.
Before it was powered up I checked the ESR of the filter capacitor and other high value caps in "bathtubs. All checked OK, but many will be "re-stuffed". When it was powered up, slowly with the use of a variac, the AVC came full on, indicating the probable leakiness of C-204, a common problem. That cap was replaced with a dipped mica 100pf unit, and the problem disappeared. All bands are operable, tho' sensitivity falls off on the higher bands. The bias voltage measure about -68vdc, it's desireable to have it near -60, and some changes were made which brought it to -61.
The PTO was off about 16 kc end-to-end. There is an adjustment which can be made externally if it is only 3-5 kc off, but this much will require the removal of a turn from the compensation coil in the PTO. There are also 2 bypass caps and one feedback cap in the PTO which should be changed if they have not been done previously (it appeared that the seal on the PTO had not been broken).
2 of the 3 caps that were replaced, the new brown discs, the old "vitamin Q's" on the bench.
The brown tube under the clip is the feedback cap, to be replaced with a dipped mica. It tested leaky when removed.
------------ desired --- 2000.00 2100.00 2200.00 2300.00 2400.00 2500.00 2600.00 2700.00 2800.00 2900.00 3000.00
initial actual --------- 2000.00 2099.41 2198.62 2297.57 2396.06 2494.48 2592.85 2691.10 2789.11 2887.74 2986.52
final, after 8 adj. - -- 2000.00 2100.31 2200.71 2300.94 2400.59 2500.22 2599.54 2699.11 2798.52 2898.63 2999.06
initial readings show that there was 13.48kc end-to-end error, and as much as 1.63kc between adjacent 100kc points.
final readings show 0.94kc end-to-end, and no more than 0.66kc between any 2 100kc points.
I have re-installed the PTO, dial and front panel. I have installed the product detector mods. basically using Lankford's circuit, with minor differences, documentation will be prepared for that and the small AVC mod which also has been made. The prod. det. mod replaces the 6BA6 BFO tube with a 6BE6 which is used as both BFO and mixer. Use of the prod. det. is essentially transparent, there is no difference in the front panel controls, the only difference is the ability to use the AVC system when the BFO is in operation, allowing much better reception of single sideband and CW signals. The AVC mods allow fast attack time and extended "hang" time. I also "re-stuffed" the associated 3-section bathtub, C-205, using disc ceramics, 0.1 @ 100vdc. Each section only sees bias or AVC voltage, no more than 75v. The originals had checked OK on the megger, but thought it'd be a good idea to make sure it stayed that way with future use. "X-Y" bypass capacitors will be installed at the AC line cord.
The other 5 bathtubs have now been re-stuffed, as has the HV filter capacitor can. Again, all checked OK, but as the date codes were in the early 1950's it was felt best to replace them.
There are several types of electrolytic can construction. This receiver has one made by Aerovox, another R-388 had one from Sprague. The differences are in the base type, and the method of connection of the capacitor leads to the external terminals. Outside another difference is evident after opening. The Aerovox must be cut open just above the base, leaving some aluminum can below the cut. The Sprague will allow the base to be removed from the bottom end. The Aerovox must be closed with a bead of epoxy, the Sprague can have the base re-inserted into the bottom, and the end of the can re-swaged over it.
The Sprague is on the left, the Aerovox on the right.
Cosmetic work takes up several days --
The band dial had been "modified" by a previous owner, strips denoting the amateur bands, as well as yellow "stickies" denoting SW stations had been added. One area of numbering had been damaged and re-inked by hand, some areas were faded. A new overlay will be applied.
these show the panel after it has had several spot treatments of mottled areas. It always looks good when wet, the mottling shows up after drying. I think it's the different reflectance of the dirt that's embedded in the wrinkle finish. When the bezel & knobs are replaced it will look very good. The "half moons" at the rack-mount screw locations will be touched up.
I think (my wife suggested it) what happened was that someone gave it a spray coat of "clear lacquer" or something like that. It was farily even, but not under the knobs, etc. It was on top of the knobs. If I hadn't tried to clean it up as I usually do we probably wouldn't have noticed -- until I removed the knobs to get the panel off. I did replace the black plastic bezel around the kc & MC dial windows with one from another R-388 because it was too much of a pain trying to get the clear coat off right now.
this is the "grungy" area near the power transformer, after the side panel has been removed for easier access. You can see an area of corrosion at the bottom rear of the side panel, that may be from the "grunge", it may have been something spilled inside the receiver. It was stuck very hard on the chassis, not soluble by mineral spirits, almost like varnish (or CocaCola?). It was over the MFP coating, so it appeared long after the MFP.
Grunge is gone, but it took some work.
Here's the product detector circuit, published in Hollow State News by Dallas Lankford, and a modification to the break-in circuit made by a previous owner. This is a nice mod, it allows the receiver to be muted simply by connecting terminals 1 & 2 on the break-in terminal strip, and the fellow who did it (in 1975) was nice enough to make a sketch and leave it inside the radio (shown below). This puts 6 vdc power on the internal relay. It is also partially noted on the schematic that is on the inside of the cover.
I added a 1.5mf capacitor across C-205B to increase the hang time of the AGC, and the diode an series resistor, similar to Orr's suggestion. I felt that 1.0mf was not large enough after trying it.
I have been using this receiver as a "listener" in the shop now for about a week, as I have been working on it, and am happy that it's "done". I actually used it on the air with my Viking 1 transmitter to make two contacts on 40m AM ysesterday.
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