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Very Nice 8R-40 Incoming!
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I figured it was time to take a break from Heathkit Transmitters, and such, so my brain could rest for a while.? I thought what better way to rest up than going through a Hallicrafters receiver that was different than the ones I have.? I picked this 8R-40 for a pretty decent price and it looks great and even has all of it's knobs, which is a rarity for me.? It should be here by weeks end and I'll get the caps ready! :-)
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Here one of the FleaBay pics...
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73
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Justin B. KI5GKD |
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The 8R-40 information on the Web indicates that its chassis is laid out
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essentially the same as my S-40B with the exception that the 5Y3 is replaced by a solid state rectifier so the 8R-40 has only seven tubes. It does have a BFO. I haven't compared the schematics other than that. 73, Maynard W6PAP On 7/31/24 06:18, John Meade W2XS wrote:
It looks to be in nice shape. Good luck with it. It looks like an S40B |
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Lots of radios had phono jacks. Partly to operate from a crystal
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phono pickup and also most of them put out audio from the detector for use in an external audio power amp. Crystal pickups had very high output, their primary reason for existence. Crystal phono pickups and microphones eliminated the need for a stage of audio amplification, an important economy. The quality of the better ones was pretty good but they were soon supplanted by other types especially after the advent of the Lp record, which needed better quality and gentler handling. I am old enough to remember when 78s were the primary kind of record; if you liked a record and played it a lot you often had to buy a replacement because the old type pickups would grind the grooves to dust. Most used steel needles, good for maybe three plays, then turned to chisels. On the record label "For best results use Columbia Needles". On 8/1/2024 9:19 AM, Justin Bowser - KI5GKD wrote: Looking at the schematic it seems almost identical to the S-40B with the -- Richard Knoppow Los Angeles WB6KBL SKCC 19998 |
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Seems to be a "gussied up" S-40B.? This is labeled? Run 2 and was built Sep 17, 1953.? I've started r-capping it and will finish up when my cap stock is replenished next week.? My wife actually likes the looks of it but I think it's because it's not all beat up like the rest of them! ? Here's a couple of pics.
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73,
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Justin B. KI5GKD |
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One interesting difference between the S-40B and the 8R-40 is the use of
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the tone control to control tone, BFO, and AVC. These are all separately controlled in the S-40B. When the control is set to "C.W." on the 8R-40, the tone control network is set the same as for "HIGH." If one is using no external CW filter, "LOW" might be a better choice. That works well for me when using the S-40B with an Elmac AF-67 for CW. I haven't, though, compared the different runs of the 8R-40 to see whether this arrangement persists throughout production. 73, Maynard W6PAP On 8/3/24 19:59, Justin Bowser - KI5GKD wrote:
Seems to be a "gussied up" S-40B.? This is labeled? Run 2 and was built |
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Run 1 of the 8R-40 used the same tone control arrangement as run 2. I have an example of the first run and the main difference is that run 1 used a selenium rectifier in the power supply and a different power transformer with two 6.3 volt ac windings.? Don't know why Hallicrafters went this route, maybe they had a bunch of transformers from a different product to use up and were trying to save a buck?? For run2 they went to the same transformer and 5Y3 rectifier as in the S40B.
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Les |
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I have to look at the 8R-40, does the control turn off the AVC when
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the BFO is operating? Does not on any of the S-20R/S-40 series. The HQ-120-X and its successors are wired that way, manual RF when the BFO is turned on. Not an arrangement I like very much. Evidently, the 8R-40 and S-40 were built for different markets. I wonder who the 8R40 was intended for. Where were they advertised? On 8/4/2024 6:09 AM, Maynard Wright, P. E., W6PAP via groups.io wrote: One interesting difference between the S-40B and the 8R-40 is the use of -- Richard Knoppow Los Angeles WB6KBL SKCC 19998 |
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Yes, the tone control switch disables AVC when set to "C.W." I prefer
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the independence of control that the S-40B provides. But one advantage of the 8R-40 might be the open switch contact on the tone control wafer when the switch is set to "C.W." It might be a good place to mount a relatively narrow filter for CW operation. Of course, what looks good on a schematic might be terribly difficult in the actual physical receiver. 73, Maynard W6PAP On 8/4/24 16:34, Richard Knoppow wrote: I have to look at the 8R-40, does the control turn off the AVC when |
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Hi, Justin,
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The point where the "extra" contact is located in the 8R-40 is following demodulation and is at audio frequencies where the 9 MHz filter on Aliexpress would not work. Most commercial audio filters provide appropriate attenuation to signals passed through them. In the case of the 8R-40, unlike those "pass through" filters, you need a network paralleled across the audio circuit. You would want something that would provide low impedances at frequencies you want to attenuate. Providing a high impedance at the desired frequency and lower impedances across the rest of the audio frequency band might be achieved by using an audio frequency parallel tuned circuit, resonant at, say, 800 Hz or some other frequency comfortable for CW copy. You would design the Q of the tuned circuit to produce the CW bandwidth you would like. 73, Maynard W6PAP On 8/5/24 13:31, Justin Bowser - KI5GKD wrote:
Maynard - What about something like this?? I ordered it when I was |
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Hi, Justin,
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The point where the "extra" contact is located in the 8R-40 is following demodulation and is at audio frequencies where the 9 MHz filter on Aliexpress would not work. Most commercial audio filters provide appropriate attenuation to signals passed through them. In the case of the 8R-40, unlike those "pass through" filters, you need a network paralleled across the audio circuit. You would want something that would provide low impedances at frequencies you want to attenuate. Providing a high impedance at the desired frequency and lower impedances across the rest of the audio frequency band might be achieved by using an audio frequency parallel tuned circuit, resonant at, say, 800 Hz or some other frequency comfortable for CW copy. You would design the Q of the tuned circuit to produce the CW bandwidth you would like. 73, Maynard W6PAP On 8/5/24 13:31, Justin Bowser - KI5GKD wrote: Maynard - What about something like this?? I ordered it when I was |
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It might make a good filter for a radio with a 9 MHz IF. None of mine
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use that frequency. 73, Maynard W6PAP On 8/5/24 18:17, Justin Bowser - KI5GKD wrote: I didn't have this radio when I ordered the filter.? I ordered it on the |
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As an alternative to adding another filter, you could set the 8R-40's
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tone setting to LOW by adding a jumper wire between the vacant CW terminal on the tone wafer of the switch and the LO terminal. That would make the 8R-40 operate CW the way I usually operate my S-40B. 73, Maynard W6PAP On 8/5/24 17:04, Maynard Wright, P. E., W6PAP via groups.io wrote: Hi, Justin, |
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