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Old 21st Jun 2020, 3:45 pm   #21
WaveyDipole
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Default Re: Kriesler Beehive radio

The triode anode current measures at 3.5mA. The reading does seem to be consistent with the valve data (attached) for a Mullard ECH35, although having limited experience with valve characteristics I stand to be corrected.

Since I have now completed replacing all wax paper and electrolytic capacitors, I have taken the variac out of the equation and am powering the radio at full mains voltage via a 240:240 isolation transformer.
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Old 22nd Jun 2020, 2:31 am   #22
petervk2mlg
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Default Re: Kriesler Beehive radio

The attached circuit might be easier to read. There are several variations of the circuit for this radio.
Note that this is a reflexed radio.
Peter
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Old 22nd Jun 2020, 10:37 am   #23
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Default Re: Kriesler Beehive radio

Peter, that is so much better! Thank you.

BTW, not doubting you, but I thought reflex receivers were built around a single valve that did everything to keep the cost down?

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Old 22nd Jun 2020, 11:03 am   #24
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Default Re: Kriesler Beehive radio

A reflex receiver is any set where the signal is amplified at RF (in this case IF) and AF by the same stage. Here the 6G8G DDP is a really busy bottle with IF amp, AGC detector, AM detector and audio preamp all going on inside. It turns an otherwise short superhet into a typical 4+R receiver.
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Old 29th Jun 2020, 8:53 pm   #25
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Default Re: Kriesler Beehive radio

I have received a replacement ECH35 and it seems to provide a much stronger LO signal than the original one which would therefore seem to have lower emission. I also discovered that the oscilloscope probe was loading down the oscillator circuit causing it to not oscillate at times. If I simply place the probe next to the decoupling cap, then it picks up oscillations across the entire band so I think the LO is probably OK now.

Unfortunately, the radio has started motor-boating particularly at low volume and I am not picking up any stations. Receiving has been a bit hit and miss, sometimes picking up audio but often just warbling or howling noise so there may be some intermittent fault or the alignment is out. Since I have no alignment information I am not sure how to proceed. With a superhet one usually aligns the IF by injecting a signal at the IF frequency and peaking, then aligning the LO to match the dial. Is it the same with this reflex receiver, or is aligning the IF different?
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Old 1st Jul 2020, 8:30 am   #26
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Default Re: Kriesler Beehive radio

Make sure the 6G8G is properly shielded and that all bypass caps are good.
IF is 455 KHz on this set. Alignment procedure is as per usual as you describe
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Old 1st Jul 2020, 9:28 am   #27
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Default Re: Kriesler Beehive radio

Peter, thank you. The 6G8 does have a metal shield around it and the resistance to chassis is well below an ohm. All paper caps around the 6G8 have been replaced. I had a peek inside IF1 and there appear to be no paper caps inside, just mica types. The reason I ask is that there seems very little effect when adjustments are made on the base or top of either IF, i.e. no obvious audible peaking effect, although there is an effect on the frequency and intensity of the motorboating. I am going to try a visual approach today by injecting a swept signal and having a look at what the peak looks like on the oscilloscope screen.
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Old 1st Jul 2020, 12:04 pm   #28
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Default Re: Kriesler Beehive radio

Some progress at last! The two IF cans were peaked at 455kHz visually using a sweep signal from 425kHz to 485kHz. Both seemed to be quite a bit off the mark. Once that was done, there was still no audio output except heterodynes and motor-boating when the volume was at its lowest point. At this point with the radio still powered on, I accidentally knocked the oscillator valve and the radio spring to life for a moment. Sure enough, by gently pushing on the valve it was possible to get clear reception! Prodding around at the base I discovered that the source of the problem was a large resistor that was wedged between the valve base and the adjacent trimmers. It was a very tight fit. The solder joints looked sound but I took it out and re-positioned it so that it was clear of any surrounding components and this seems to have solved the problem. Perhaps the one of the joints was bad or the resistor body was making contact with one of the valve tags or trimmers? Whatever the case, the radio is now receiving quite well on both MW and SW and there is no motor-boating.

At this point I was using the replacement oscillator valve, but as a test I put the original ECH35 back without moving the tuning and was met with silence. Hunting around a little with the tuning control is was possible to pick up the station but very faintly. Putting back the replacement ECH35 made a big difference. This appears to confirm that there is definitely a problem with the original ECH35 valve.

I intend to replace the original volume control with a switched pot to provide an On/Off switch as there is none at present and will use the original volume control to re-instate a proper tone control arrangement.

There is another question I would like to ask. The 6G8 valve envelope is somewhat loose within its base. I was very careful when I removed it so as to apply pressure to the base only. The valve looks OK when running and there is no unusual deposit or discolouration within the envelope so presumably the glass envelope has simply come away from whatever adhesive was used to secure it to its base? Presumably also, so long it has vacuum it should remain OK?
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Old 1st Jul 2020, 5:29 pm   #29
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Default Re: Kriesler Beehive radio

Spoke to soon it seems.

I simply swapped the 0.5 meg volume control pot for a 470k switched pot and its gone back into the heterodynes + motor-boating mode again. I didn't expect that to make any significant difference, but something is amiss, although I can't seem to find it. The LO is producing a sine across both bands. I get an IF of 455kHz at the output of the mixer and input of the first IF can. Feeding in a 455kHz signal modulated with 1kHz produces a clear loud tone. However there is no response when I touch or bring my hand near to the antenna wire. Both sections of the variable capacitor seem to test OK, coils test good, band-switch tests good and that resistor I moved seems to test good so I am stumped for now.
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Old 2nd Jul 2020, 7:50 am   #30
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Default Re: Kriesler Beehive radio

A loose base won't have any effect on the vacuum. Bases regularly come loose. I usually reglue the base using a thin bead of two part epoxy. Others may well have different solutions.
Re the capacitors in the IFT...these will be mica types and well worth checking. If they are leaky you won't get a good peak.
Australian radios of the period almost never had a power switch fitted.
It sounds to me as if there are random connection problems in your radio. Well worth going over the circuit and checking all resistors and soldered connections. Simply changing the volume control shouldn't have produced the effect it has.
Make sure that the AGC bypass capacitor is good and soldered into position well.
It sounds like your radio is capable of working well, so no catastrophic problems there.
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Old 2nd Jul 2020, 12:56 pm   #31
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Default Re: Kriesler Beehive radio

Looking at it again this morning with your comment in mind and a fresh pair of eyes and the problem was spotted straightaway. It was indeed the AGC bypass cap that had broken away at one end. Although I had a good look around yesterday evening, the joint to the tag on the socket is rather concealed under the cap and my pre-occupation with the LO/mixer valve section was perhaps something of a distraction. In any case, your comment focussed my attention on appropriate area and the problem was quickly found so thank you for that.

Does anyone have the alignment instructions for this radio?

I couldn't find them anywhere online. I get the general idea but one aspect of it is puzzling me as there seems to be insufficient range on one of the bands. It could be that one or more capacitors in the tuned circuits needs tweaking but it would be useful to know the exact alignment frequencies to use and what constitutes the alignment marks. There are some numbers for the SW band, but nothing really to go on for the MW band.
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Old 3rd Jul 2020, 11:27 am   #32
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Default Re: Kriesler Beehive radio

What I would do is align the two IFTs at 455 Kcs Then on the B/C band set the gang at minimum capacity (wide open) and feed in a signal of 1650Kcs. Use the oscillator trimmer to set the signal at that point. If you like you could then use a signal of 1404Kcs and set the pointer at 2PK (its a NSW station).
Bottom end of the B/C band (gang fully closed) can be peaked at 540 Kcs using the oscillator coil slug.
With the SW band I'd just peak it with a signal input of 18MC. It's not a communications receiver and do you really plan to listen to any SW stations?
I attach a pdf about the mods for this model. Maybe you already have this.
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File Type: pdf kriesler11-4_with_revisions-ver2.pdf (3.59 MB, 61 views)
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Old 4th Jul 2020, 12:36 pm   #33
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Default Re: Kriesler Beehive radio

Thanks. The IF alignment at 455kHz is already done but I had missed that oscillator coil slug. The process on both bands was a bit confused because of imaging (at least two instances of the modulated signal) but I think I have sorted it out now by looking at the LO frequency which, I believe, should be the signal carrier frequency + IF frequency when correctly tuned. The image appears when LO frequency = signal carrier frequency.

What I also hadn't realised was that the trimmers need to be tweaked in pairs to tune the top end of the band. I has assumed one tweaks the top and the other the bottom.

The bottom end of MW is at about 530kHz. Turning that slug did not seem to make much difference. There is a corresponding screw for the SW side which I presume tweaks the bottom end of the SW band, although the slug does not appear to mesh with the SW coil like the broadcast band one does.

In any case, I think I have the general idea. I don't have '2PK' marked on the dial, but I do have PK. Is this the same?

Last edited by WaveyDipole; 4th Jul 2020 at 12:47 pm.
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Old 4th Jul 2020, 2:23 pm   #34
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Default Re: Kriesler Beehive radio

If you look at the dial there is a big 2 on top at left and right ...2 signifies NSW stations. So yeah the PK is 2PK broadcasting on 1404KCs. I use 2CR on 549 to peak the low frequency end of the band. Adjusting the B/C oscillator coil slug should peak the low frequency signal. The radio has a fixed padder capacitor so you can't adjust that. From memory the padder is 470 pf or so. Putting a trimmer in parallel would enable you to adjust its value. Alignment is just the standard procedure in my view.
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Old 4th Jul 2020, 4:42 pm   #35
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Default Re: Kriesler Beehive radio

Yes, I now understand what you mean. I am simply not familiar with the Australian dial layout. I now have it so that it 549 is on 2CR, but can't quite get the 1404 on 2PK, but it is close enough. I might try a trimmer in parallel with the padding capacitor as you suggest. Thank you for the Australian perspective. I see you are from Parkes, so perhaps near the home of the famous dish?
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Old 5th Jul 2020, 1:39 am   #36
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Default Re: Kriesler Beehive radio

I wouldn't worry about the dial not being 100% accurate.
The Parkes Radio Telescope is a few km out of town, yes.
Actually I'm English, but have lived in Australia for many years.
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Parkes, NSW Australia

Ex, High Wycombe, Colchester, Nottingham, Chester, Herts, London!)
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Old 6th Jul 2020, 12:31 pm   #37
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Default Re: Kriesler Beehive radio

Fair enough. It seems to be working very well otherwise considering my makeshift antenna (maybe 3 yards of mains flex thrown over the shed roof) so perhaps best left alone. Time to concentrate on the case.

This example is painted cream (aged white?) and definitely needs cleaning up. Some of the various segments have crack, both previously fixed and one clean break all of which will need to be fixed. There is also a hole to fill in. I guess it will need re-painting afterwards so perhaps best stripped down completely and repainted once repairs have been done? I have not had to repair cracked Bakelite before so this will be a new challenge to carry out nicely.
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Old 7th Jul 2020, 2:47 am   #38
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Default Re: Kriesler Beehive radio

Can you post some photos? Does it have the original knobs? There was a factory painted cream model.
Most ones sees are the brown bakelite.
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Old 7th Jul 2020, 10:04 am   #39
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Default Re: Kriesler Beehive radio

A photo can be seen here:

https://www.vintage-radio.net/forum/...light=Kreisler

In the photo you will see that it did have all four knobs when I collected it. I put it directly in the boot of my car. It was late evening and dark when I got home. I parked up on the drive, took the radio out of the car and walked with it directly to the shed, stopping only to open the side gate and then the shed door, and placed it on the floor. When I looked at it the next day in daylight, there were only three knobs with the fourth nowhere to be found! I had searched driveway, car and shed floor several times but to no avail. The member I picked it up and his wife also had a look on their drive but also found nothing although he thinks he may have found a grub screw so this may explain how the knob came adrift from the radio, but as to where it went, its a bit of a mystery. If it ever turns up I will be very happy but that is now looking rather unlikely.

The Bakelite itself is brown but has been painted over.

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