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   Home   Help Search  
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Author Topic: Heathkit SB400 versus 401  (Read 25209 times)
N4NYY
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Posts: 5224




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« Reply #15 on: October 04, 2011, 04:43:40 PM »

Mike,

I am trying to join the Heathkit Yahoo Group to see if someone has an IG-42 manual in full size. I have one shrunk to 2 pages onto one. But I have not gotten approved.
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W5RKL
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Posts: 1113




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« Reply #16 on: October 05, 2011, 10:50:32 AM »

Mike,

I am trying to join the Heathkit Yahoo Group to see if someone has an IG-42 manual in full size. I have one shrunk to 2 pages onto one. But I have not gotten approved.

Vincent,

I have an update on your membership application to the Yahoo Heathkit Group. Send me a private e-mail.

73s
Mike
W5RKL
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W5RKL
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Posts: 1113




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« Reply #17 on: October 05, 2011, 10:53:41 AM »

Vincenzo (N4NYY)

I addressed you as "Vincent". I apologize.

73s
Mike
W5RKL
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AC5UP
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Posts: 4546




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« Reply #18 on: October 05, 2011, 12:09:08 PM »

If you really want to get on Vinnie's nerves, show up at his house on Halloween dressed as a 6SK7 metal tube.

Dude can't deal with metal tubes...................................
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N4NYY
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Posts: 5224




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« Reply #19 on: October 05, 2011, 12:10:37 PM »

I think he would need 8 legs.
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AC5UP
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Posts: 4546




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« Reply #20 on: October 05, 2011, 12:18:50 PM »

...and an index key on little W5RKL.
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KD4SBY
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Posts: 269




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« Reply #21 on: October 09, 2011, 10:25:28 AM »

W5RKL- Mike, you seem to know a lot about the SB-400 - May be you can help me.
I got the manual now, and I can not find a clear explanation what the functions STAND BY, TUNE and SPOT do.
They are used in table form in several sections on Alignment and Operational use, but nowhere a word about what part does or does not do when these functions are used. For example, in STAND BY, what is deactivated and what is still active? In TUNE, what is happening and which circuits are involved? In SPOT, what am I spotting and which circuits are used for that? Is this only valid when I link my SB-301 to use it in the Transcvr mode or not?
I tried to trace the circuits on the schematic, but tracing through the wafer sections of the various switches is almost impossible to do.
Also, wading through the assembly and alignment instructions, where these functions may have been used at one time or another, to find the answer is rather tedious.
Hope you can enlighten me.
Thanks and 73's
Bernie.
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AC5UP
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« Reply #22 on: October 09, 2011, 12:13:04 PM »

If I recall:

STANDBY = Filament and pilot light power only with B+ and HV disabled. Think of it as a warm idle that saves warm-up time compared to full power off.
TUNE = Regardless of mode selected the TX is keyed in CW so the driver and PA tubes can be optimized for frequency and load impedance.
SPOT = Allows the transmitter VFO to be heard by the receiver so the TX frequency can be adjusted to match the RX frequency (typically for CW simplex).
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AC5UP
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Posts: 4546




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« Reply #23 on: October 09, 2011, 12:19:55 PM »

Vincenzo (N4NYY)

I addressed you as "Vincent". I apologize.

N4NYY's new nickname is: " IGGY STANDBY, THE B+ KING OF MYSTERY "

It's a long and disturbing story........ Then I realize this is the second thread in a week regarding a Heathshkit in STANDBY. What is it with you people?   Roll Eyes
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W5RKL
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Posts: 1113




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« Reply #24 on: October 09, 2011, 01:48:41 PM »

W5RKL- Mike, you seem to know a lot about the SB-400 - May be you can help me.
I got the manual now, and I can not find a clear explanation what the functions STAND BY, TUNE and SPOT do.
They are used in table form in several sections on Alignment and Operational use, but nowhere a word about what part does or does not do when these functions are used. For example, in STAND BY, what is deactivated and what is still active? In TUNE, what is happening and which circuits are involved? In SPOT, what am I spotting and which circuits are used for that? Is this only valid when I link my SB-301 to use it in the Transcvr mode or not?
I tried to trace the circuits on the schematic, but tracing through the wafer sections of the various switches is almost impossible to do.
Also, wading through the assembly and alignment instructions, where these functions may have been used at one time or another, to find the answer is rather tedious.
Hope you can enlighten me.
Thanks and 73's
Bernie.

Standby mode:

Whether operating Transceive (TRCV) or non-Transceive (TRANS), the transmitter is disabled. Filament voltage will continue to light the tubes and bias, LV, and HV supplies will continue to produce output voltages.

TUNE mode basics:

1. Disconnects microphone input to VOX amplifier V12A and grounds the speech amplifier V1A's output.
2. Grounds the CW key line plus grounds the cathode of Relay Amplifier V12B causing both relays (standby/operate and antenna change over relays) to energize (V12B conducts). A CW key is not required to produce RF output in TUNE mode.
3. Turns the CW Side Tone Oscillator OFF.
4. Connects the CW CAR Oscillator crystal (3395.4Khz) to the Upper Sideband oscillator V2B.
5. Ground linear amplifier ALC input (also in CW mode).
6. Turns on CAR OSC, Isolation Amplifier, LMO (VFO) Mixer, Transmit Mixer, Driver, and both final amplifiers.



 SPOT:

Depending on the Mode switch setting one or more of the follow circuits will be turned ON and/or OFF.

1. Speech Amplifier (USB or LSB only)
2. Carrier Oscillator V2A, V2B, and/or V2C ON
3. Isolation Amplifier V3
4. LMO Mixer V4
5. Transmit Mixer V5
6. HET OSC V8
7. Driver V9

It's impossible to hear the SB-400 or SB-401 LMO in the receiver with the Function switch set to SPOT since the LMO (VFO) operates over a 500Khz range of frequency between 5.000Mhz and 5.500Mhz. What is heard is the actual "operating" frequency whether it's the CW operating carrier signal or the USB or LSB operating signal.

73s
Mike



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KD4SBY
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Posts: 269




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« Reply #25 on: October 10, 2011, 06:40:11 AM »

Thanks for the info fellows. I am working on an SB-400 with no RF output and this information helps. At least I know now what to expect in the varions settings of the switches. Smiley
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W5RKL
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Posts: 1113




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« Reply #26 on: October 10, 2011, 09:58:28 PM »

Thanks for the info fellows. I am working on an SB-400 with no RF output and this information helps. At least I know now what to expect in the varions settings of the switches. Smiley


Have you verified that all 3 oscillators, Carrier (TUNE/CW, USB, and LSB), LMO, and Heterodyne oscillators are all working? If just one oscillator fails there will be zero RF output.

You didn't say if loss of RF output occurs on all bands or only one or two. Therefore, is loss of RF output occurring on all bands or only a few bands?

I assume you have verified that all tube filaments are lit. Remove the driver tube shield to verify it's filament is lit. I have experienced loss of RF output due to failure in the driver circuit, loose/bad soldering connections on the tube sockets so look closely at the driver tube.

Check RF Choke to be sure they are not open. I bought an SB-401 that had no RF output. The problem was an open RF choke. The RF choke looked good but when checked with an ohm meter, it was open.

Have you verified all power supplies are working and supplying the correct voltages?

73s
Mike
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KD4SBY
Member

Posts: 269




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« Reply #27 on: October 11, 2011, 09:06:38 AM »

Yes I have verified that all power supply voltages are present and correct, and all the the tubes are lit.
And it has no RF output in any band, in any mode. It is as if the plug has been pulled.
I am  not sure if the oscillators are working. A fellow ham suggested that I take a general coverage receiver like in my IC-718 and tune it to the frequencies of the various Xtals. They should radiate enough RF to be able to be heard in the radio by using just a piece of wire. I thought that was a good idea, and I will do that.
At this point it can be anything, but I doubt if it is a tube. (Unless one is so weak that it stopped oscillating in a Xtal circuit, and I will find that out soon enough using  the method above.) Unfortunately I have no spare Compactrons, hope that is not one of those.
I checked the Plate voltage, measuring it right on the top of the 6146, and it is in the required range, so I don't think it is the RFC.
The builder did a good job, everything is neat looking and there are no signs anywhere of a sloppy soldering job.
I think also that there is someting wrong in the relay driver area. The relays click in and out in rhythm with the closures of the key in CW, and I don't think it  should do that. It supposed to be grid block keying. Besides, there is no way they can keep up with even 5 words a minute!
Have too look there.
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W5RKL
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Posts: 1113




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« Reply #28 on: October 11, 2011, 12:48:57 PM »

The reason the relays are activating (clicking) ON and OFF at the same rate as the CW key is pressed is because the VOX delay setting is set too low (very short delay). Adjust the VOX delay and hit the key to produce dits until the relays remain energized for a second. That will tell you 2 things:

1. The CW sidetone oscillator is working and is driving the VOX amplifier
2. The VOX amplifier and relay amplifier circuits are working.

The CW sidetone oscillator output is fed to the input to the VOX amplifier in CW mode. If the CW Sidetone oscillator was not working, plugging a key into the rear CW socket, Mode switch set to CW, and pressing the CW key would not cause the relays to energize.

Set the front panel meter switch to PLATE then press the CW key in CW mode, the meter should display, when the transmitter is activated, should be slightly higher than 50ma. The tells you the final amplifier is conducting with idling current.

Measure the final amplifier tube's grid voltage while pressing the CW key in CW mode. The final amplifier's grid voltage should become "less negative" when the CW key is pressed. If it does then the grid block keying in CW mode is working.

Since you do not have a frequency counter, your friends idea is a good one. The Carrier Oscillator crystals, 3 of them, are on the bottom of the transmitter next to the transmitter's control relay. The crystal frequencies are stamped on the top of each crystal. You should hear each crystal frequency if the Carrier Oscillator is working. The Heterodyne Oscillator, if heard, will produce the frequency of each crystal depending on the position of the band switch. The VFO frequency range is between 4.999Mhz and 5.500Mhz so tune the receiver with the receiver's antenna wire wrapped around the transmitter's VFO tube.

You can purchase NOS Compactron tubes from various tube outlets on the web. I use www.vacuumtubes.net as my source of tubes.

Check the transmitter circuit voltages using the manual's voltage chart.

73s
Mike
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KD4SBY
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Posts: 269




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« Reply #29 on: October 14, 2011, 06:50:29 AM »

Update - Indeed the VOX adjustment soved the problem of the relay. It is now working as it should. But that did not solve the other problem of no RF output.  I think that the problem is that the Xtal Osc. (V8A) 6AW6 is not working. I can not find an output on the plate with either an RF probe or Scope, but can hear the lower Xtal frequencies (12,15, and 22MHz)  on the shortwave receiver! Can't figure that out. I have ordered some spare tubes to be able to substitute
I can hear the Carrier freq
Also, I still can not get the meter to read any plate or grid current in any band. That might be a different problem, since I think that there is no RF needed to draw some grid current. Also the meter pins to the right when switched to ALC, I have not looked at that as yet either.
BTW I have all the usual test equipment, including several counters. But I am not sure if I can use them with the higher voltages present in tube equipment, and thus have not used them. In my case, I was not after eact RF frequencies anyway, just the presence of one.
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