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Author Topic: HBR-16 Receiver Sells for $315  (Read 22692 times)
G3RZP
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Posts: 8018




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« Reply #15 on: July 13, 2012, 03:56:27 AM »

The 6EH7/EF183 really needs an unbypassed 27 ohm cathode resistor for best results. That has a marked effect on the change of input impedance with bias, and significantly improves the IMD performance. Using a low plate load impedance helps, too - you can then get no more gain than you need while being on a relatively linear part of the characteristic. That's recommended somewhere on one of the Philips data sheets.

The Marconi Marine rx, the 'Pennant' used a 6EH7 RF amp like that with a 4 diode ring bridge mixer, and had very good dynamic range.
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K1ZJH
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Posts: 3188




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« Reply #16 on: July 14, 2012, 08:03:58 AM »

Do you remember the adapters that were sold back in the 60s to permit oddly paired radios to transceive?
I've never seen one nor encountered anyone who has any experience with them. The manual is not on BAMA.
Were there others?

73 de jim, N2Ey
 


I've never seen one myself. I always wondered how well they actually worked!

Pete
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KB1WSY
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Posts: 1276




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« Reply #17 on: July 14, 2012, 03:02:09 PM »

Short of building a CW *trans*ceiver, what's the best linkup for vintage, tube based, "separate" homebrew gear? I don't mean the *simplest* linkup (for instance a knife switch for T/R), but the *best* with the aim of achieving fulll QSK operation. Here's my current plan:

--HF RX.
--HF TX initially XTAL controlled.
--HF VFO (when I have time to build it) w/ relay based keying of TX (what is the quietest relay, reed presumably? I don't like the idea of relay "clatter" noise).
--Electronic T/R switch (there are 3 or 4 designs for tube T/R switches in ARRL literature from the 1960s).

Informed by my reading of the vintage literature, this approaches the convenience of an actual transceiver, except for the need to tune the RX and TX individually. Unless you're competing in contests, this is almost as good as a transceiver.

Comments?

73 de Martin, KB1WSY
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N2EY
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Posts: 4387




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« Reply #18 on: July 16, 2012, 08:08:07 AM »

Short of building a CW *trans*ceiver, what's the best linkup for vintage, tube based, "separate" homebrew gear? I don't mean the *simplest* linkup (for instance a knife switch for T/R), but the *best* with the aim of achieving fulll QSK operation. Here's my current plan:

--HF RX.
--HF TX initially XTAL controlled.
--HF VFO (when I have time to build it) w/ relay based keying of TX (what is the quietest relay, reed presumably? I don't like the idea of relay "clatter" noise).
--Electronic T/R switch (there are 3 or 4 designs for tube T/R switches in ARRL literature from the 1960s).

Informed by my reading of the vintage literature, this approaches the convenience of an actual transceiver, except for the need to tune the RX and TX individually. Unless you're competing in contests, this is almost as good as a transceiver.

Couple of points:

1) VFO control is much more important than QSK.
2) Having to zero the tx to rx really only makes a difference in contests and other time-sensitive operating. For general QSOs, it's not such a big deal.
3) It is best to get experience with a good working non-QSK station before attempting QSK.
4) Keyed VFOs tend to be chirpy and have other problems. Diode noise in the final amplifier can be a problem, as can harmonics generated by electronic TR.
5) A single 3PDT relay in a small box can handle all TR functions in most hollow-state stations. First contact switches antenna, second grounds rx mute line on receive and tx VFO line on transmit, third grounds rx antenna input on transmit and can operate other functions on receive.

IOW, start simple and straightforward. Rx, tx, TR relay, VFO, antenna. QSK later.

That said, I did have a full-QSK tx/rx setup in the 1970s. It worked like this:

- Homebrew rx shown on HBR website
- Matching tx with Class C final, grid-block keyed.
- VFO for tx used heterodyne principle. Both oscillators ran all the time, mixer was grid-block keyed. Tunable oscillator around 5 MHz, xtal oscillator around 9 or 12 MHz for 80/20 and 40.
- Keyed highspeed relay did muting and tx keying duties (small surplus relay meant for keying, not a reed nor a mercury-wetted. SPDT with moving contact grounded.)
- Electronic TR by means of 6AH6 inside transmitter. Connects to final via small high-voltage capacitor. See transmitter article in QST about 1971 (The T-9er or some such was the name).

73 de Jium, N2EY
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G3RZP
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Posts: 8018




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« Reply #19 on: July 16, 2012, 11:39:16 AM »

I have never got on with true QSK. For me, key controlled changeover is better.

I have plans for a rebuild of a really basket case HRO I picked up - when I get another project or two sorted and first, repairs to one of the workshop benches. Getting at that is a major exercise..

The HRO rebuild is aimed at ham bands only. Set of 1.4 MHz crystal filters that I happen to have (USB, LSB, AM, 3, 1, and 0.2 kHz for CW). Then convert to 85 kHz so there's not too much gain at 1.4 MHz. 6EH7 triode connected RF amp with low plate load resistance to give just enough gain, a bandpass coupled pair, a 6DJ8 mixer, a 6C4 oscillator, the filters a 6EH7 amp, a 6EA8 mix/osc to 85 kHz, a 6BA6 amplifier at 85 kHz, a 6AU6 BFO/product detector, a 6EA8 triode as infinite impedance detector for AM, pentode as calibration osc, a 6AT6 as AGC rectifier, AGC DC amplifier and S meter driver and a 6BM8/ECL82 AF and output. Stabilised heaters for the 6DJ8, 6C4, 1st 6EA8 and 6AT6 using transistors and B+ lines of 105 and about 180 to keep heat down. Built in PSU, a notch filter and an antenna attenuator.

Should be an interesting exercise producing a long chart frame to give a 'slide rule' dial/ frequency graph, but that's work for the milling machine....More problematical will be getting the necessary machine for engraving the new dials on the HRO knobs. Not sure if I will go for nickel silver for the metal skirts or aluminium. A new etched custom name plate will be $50. but hopefully will be worth it..

A fair number of hours have gone into calculating how to get reasonably linear dial calibration. The answer seems to be a biggish padding cap across the tuning gang and then a series capacitor.

Another long term project. A good job my current plans are to retire in summer 2013...but it might depend on whether there are financial incentives to carry on working that I can't resist.
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K1ZJH
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Posts: 3188




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« Reply #20 on: July 19, 2012, 11:37:24 AM »

The old Johnson T/R electronic TR switch would be ideal for QSK.  You'd still need a way to mute the RX (maybe open the
RF/IF gain control?) during TX.  I tried my Johnson TR unit on my HT-32 and SX-101A setup, but since the HT-32 always
runs the driver and PA in class AB1, even during standby, the receiver noise floor was raised by several dB. The biggest problem with relays and QSK is to get the timing right. The TR relay has to be fast to avoid any hot switching. 

I'm now using an Omni VI with full QSK with a heavily modified SB-220 amp.  QSK is the cat's meow when running
spilt on CW. I could never go back to clanging relays or long delays.

Pete
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