I guess it's a judgement call whether this goes in the transistor radio forum or not. I have an FRG7 that is extremely un-sensitive. I can force a signal from a signal generator through it but there are barely any stations audible, and the volume is way too low. It has plenty of birdies, however. I've replaced Q101 with a pricey replacement NTE454 but to no avail. Voltages from the 9 volt regulator seem pretty normal, but voltages from Q411, the 10 volt regulator are around 15 % high. I'm running it off 120v ac. I tried measuring the voltages on Q411 while I reduced the input voltage with a variac and found that it regulates about 15% high even when I reduce the input voltage to 100 volts. At 100 volts I measure the normal voltage of 13.5 volts at the collector while the base and emitter still read 15% high. The 390 ohm resistor across the base and collector measures about right when measured in-circuit. That leaves the zener diode D412 as a possible culprit, as well as Q411 itself. I haven't messed with zener diodes before and I know little about them. I don't know if getting the 10 volt supply down where it belongs will fix the radio, but I have read that some of the components are not very tolerant of high voltage -- for instance the transformerless audio output stage. Any ideas?
-DS

I guess I'm answering my own question after a fashion. I found an NTE replacement which is cheap and available: NTE151A. So I guess I'll order a couple and see if that helps.
-DS

Don't worry so much about the voltages, any good design can run with voltages off by 25%.

I'd work on the sensitivity issue. Try moving your signal generator to the base of the first RF transistor, through a 0.01uF capacitor. Then to the collector, then so on down the radio. The signal should be at elast 4 times as loud at the base compared to the same transistor's collector. It should be able the same loudness going from the collector of one transistor to the base of the next.

That should help you narrow down the problem to one stage or interstage.

I think that's what I'll end up doing, but only after I sort out the voltages. This is complicated by the fact that there are some errors I've identified in the manual and some places where the manual doesn't match the schematic. I'm measuring a little more than 11.5 volts across an 11 volt zener diode attached to the base of a transistor that's supposed to be at 10 volts. (voltages are relative to chassis ground.) I'm finding that working on a transistor rig is more challenging than a tube rig due to the pinout schemes and the problem of finding the right places to measure a component underneath a pcb. (There are some components that can be measured from the top using a fine grabber probe, but not all.)
-DS

Doc,

And the other big difference in the solid state rig is the ease of causing component damage if your probe accidentally shorts the wrong two points together. I think the closest thing to this in a tube type set is the ease with which a string of tubes in a battery type set can be blown by a poorly placed probe.

With the symptoms you are seeing, low sensitivity and birdies, I wonder if something is going on with the oscillator output of the Wadley loop system?

Rodger WQ9E

I had typed a fairly lengthy response but something timed out and I lost it all! So this will be shorter. I thought that since the lock lamp was extinguishing properly all the stuff up to that point was working okay. But the worst birdie is on the harmonics of 1 MHz and it gets much stronger down in the broadcast band, so maybe you're right, Rodger. I had missed that earlier because the dial calibration is off by a full 20 khz! I had thought the birdies were at 7020, etc.
-DS

The spur at 1 Mhz. intervals is perhaps the major annoying issue with the Wadley loop system so that is probably normal. These are the harmonics of the 1 Mhz. oscillator and will be stronger the lower you go in frequency. If the front end gain is reduced then that signal will be more noticeable.

The oscillator outputs (feeding the first and second mixer) are probably OK. From the earlier post I thought you had numerous birdies that weren't part of the 1 Mhz. oscillator.

At this point I wouldn't worry about any voltage that is within 20% of stated value because any deviation within this range won't be responsible for a major sensitivity loss. If you have a scope and a decent signal generator, signal tracing is probably the fastest method to find the issue in your FRG-7

I have a FRG-7 but I don't think I have ever been inside it, it worked when I bought it and still works fine. My Racal RA-17 required the most work of any of my Wadley loop receivers because a previous owner mechanically damaged one of the tunable oscillators and I had to replace that part. My Barlow Wadley XCR-30 had a little problem in the BFO and my Kyoritsu RA003B (which implements a Wadley system in a way I still don't full understand) had a problem with the servo tuned front end but in general one of the beautiful parts of the Wadley loop is its simplicity compared to a PLL/VCO synthesized system.

Two other thoughts:
1. Maybe the original front end FET you replaced was bad and the original owner tried to "align the problem away" before giving up on the receiver. I have run into this issue before so it may be severely out of line killing the gain.
2. It is possible that the new FET was defective when you got it. It is unlikely but not impossible, a small percentage of new parts are defective and you may have won a lottery you didn't want to win. I have restored a lot of gear and have found a new production #47 pilot lamp that had a shorted base, a couple of new dipped mica caps that were a dead short, and an entire pack of capacitors that had the +/- markings reversed.

Good luck!
Rodger WQ9E

.

It's kind of ironic that tubes are getting easier to find than some transistors. That's why I spent 4 dollars on an Allied AM/FM/SW 15 transistor radio this weekend. This FRG7 was one I thought I'd use for parts for another FRG7 that I bought recently that is working properly. But now I'm trying to see if I can repair it. Maybe between my two more or less working signal generators and my three more or less working scopes I can do some more troubleshooting. The 1 MHz birdie is not noticeable on the good FRG7. It seems like replacing the three 1000mfd electrolytics yesterday helped, and I have the other 12 smaller electrolytics to replace. I may get to some of those today.
-DS

The replacement zener diode arrived and I installed it today. I think the main problem is with the power transformer: when I ran the radio on 120 volts the lock lamp wouldn't even come on. When I reduced the line voltage to 100 volts the lock light began to function normally and there were some stations that could be heard. I decided to try operating the set off my DC power supply and found that when running on DC it operated almost normally. There were plenty of stations and I could copy SSB easily. That's the most progress I've made with it so far. I measured the voltages at Q411 and found them to be close to what the manual says they should be when running it on DC. I conclude that the voltage levels are pretty critical in the FRG7 and that the biggest problem with this set lies in the power transformer.
-DS

Transformers are constrained to transform according to the turns ratio, exactly. There is no way for a transformer to put out an extra even 0.00001% more voltage than it was wound for.

So I would look elsewhere for the problem. Most likely, the series pass transistor is very leaky or shorted. Check the voltage at the collector, emitter, and base of the 2SD313 witherhetransistor removed. The base should be at the zener voltage. When ou plug in the transistor, the base voltage should drop maybe atenth of a volt. The emitter should be about 0.7 volts lower than the base. The emitter should be several volts lower than the collector. If the base voltage goes UP when you plug in the transistor, the transistor is very leaky. If the emitter is very close to the collector voltage, the transistor is shorted. Good luck.

Wouldn't some shorted turns in the primary have the effect of increasing the turns ratio, thus a higher voltage in the secondary? Having said that, I did look at Q411 and it has been replaced at some time in the past. It looks like a "D325" substitution, not a "D313." Also, I found and removed what appears to have been a solder bridge in the vicinity of D413 and R451.
-DS

A shorted turn or turns then the transformer will in effect have a shorted secondary. At best it will blow the mains fuse. At worst it will get very hot. Even worse if you have a short between primary and a secondary - doesn't happen often with power transformers as there is usually a bit of elephant paper between the two, but I have seen it with audio transformers.

okay, let's do this logically. Hang a voltmeter on the collector of Q411, the voltage regulator. Vary the input voltage with your variac, between 100 and 125. Note that the unregulated voltage there on the collector swings a lot, probably like from 11 to 14 volts or so.


Now move the meter to the emitter of the same transistor. vary the variac voltage again from 100 to 125.

The emitter voltage should be around 10 to 11 volts, and not vary more than a tenth of a volt or two at the very most.

If it varies a LOT, like the same swing as the collector voltage did, the transistor isn't regulating, probablly due to it being leaky, or due to the collector to base resistor being too small, or due to the base to ground Zener being no good. The voltage at the base should be steady, not vary more than a tenth of a volt or so.

There's also a second zener, D413, to regulate the really critical voltages-- if there's been a short across its series resistor R451 then the zener is toast. If the short was across the zener, the resistor has overheated and probably drifted in value. Nothing good is going to happen until you get the output of the 10V regulator regulating, and then the subsequent 9V zener regulating.

Thanks for the suggestion, Ancient. I will try the procedure you outlined later tonight. As I think I wrote above, I have already replaced the zener diode on the base of Q411. I have ordered one lot of five NOS 2Sd313 transistors from an ebay seller in Arizona. They are cheap. I do need to find some of that white goop for the heat sink, however. From previous voltage measurements I made, I concluded that the 9 volt supply was working properly but the 11 volt supply was not regulating. In previous measurements I saw that the collector of D411 was at 15.5 volts with 117 volts supplied to the set. That is why I suspected the power transformer. At the same time I measured 11.5 at the base. That's why I replaced the 11 volt zener. Finally I measured 10.9 at the emitter (which should be at 9.5 according to the manual). These are measurements that I made over a week ago. When I ran the set off a DC power supply (for the first time) yesterday, I found it to be operating almost normally for the first time since I acquired it. By "almost normally" I mean in comparison to a "good" FRG7 I have. The biggest difference between the two sets was the audio output level. My "good" FRG7 has the AF gain set at about 2 for comfortable listening. The "bad" FRG7 needed to have the audio set at at about 5 for comfortable listening.
-DS

Okay. I did the experiment suggested by Ancient. Measurements at the emitter, collector and base, respectively at 100, 110, and 120 volts:
Emitter 11.3, 12.2 13.3
Collector 12.5, 13.5, 14.8
Base 12.0, 12.8, 14.0
I also measured TP406 at the same three input voltages:
TP406 9.5, 9.7, 9.9

So I agree with Ancient Hacker that Q411 needs to be replaced. It's not the original anyway: it is something somebody substituted trying to repair this set in the past. Fortunately I already have some 2SD313s on order. I do need to get some of that heat sink compound. I've already replaced the zener, D412. R450 is well within tolerance. The measurements at TP406 tell me that the 9 volt supply is regulating but it should work better with a new 2SD313 installed. Finally, I tried operating the set at 100 volts AC input, and it worked fine except that the audio was weak as I described above. Thanks for the help, all who responded.
-DS

The stabilisation of the base voltage by the zener looks very suspect - have you checked the value of the series resistor R450?

The transistor regulator doesn't have much voltage across it, it needs more and a couple of volts to satbilise properly - agina I get back to the zener not regulating.

Hmmm, something is wrong in that regulator. Snip out the transistor and check the base voltage again. If its not very close to 10.6 volts, the Zener is bad or the resistor is much too small.

If it does stay close to 10.6, then the transistor is very leaky, almost shorted.

.