Richard,
I think you need to find the cause of the low voltage (230V vs. 250-260V) and
fix that first.
The meter circuit does not change by switching the sideband. As Garey said it's
only
job is to choose the filter and the lamp.
The low screen voltage will certainly affect the plate current.
In the X-CW mode, the carrier frequency is shifted and the side-tone is fed to
the balanced
modulator. Correct me if I am wrong, but my understanding is that since the
carrier is shifted,
this signal can only pass through the filter selected at the X position. At the
non-X position,
no signal goes through.
A lower screen voltage negatively affects the plate current. A lighter bias may
be required,
but AC-4 may not be able to supply it. Now, even in this case, if you push
signal to the control
grid, there will be some plate current. By advancing the TX gain, you did
exactly that. But
as you know that's not the idling current (we are providing input) we want to
check when
setting the bias.
If the screen voltage is not too low, you can still see a good power output.
But without proper
biasing, the linearity will suffer.
Kihwal, K9SUL
________________________________
From: Donley <donley...@comcast.net>
To: k4...@mindspring.com; drakelist <Drakelist@zerobeat.net>
Sent: Tuesday, July 12, 2011 10:57 AM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Garey,
Sorry about the delay in my response. Time gets away from me.
I acquired the TR-4C several years ago and my normal procedure is to put a new
acquisition on the bench and run it through a simple use test. Then I tag it
with the information, working or not, and put it on the shelf for later free
time. This one has no tag, so my procedure must have failed. I don't remember
if the bias worked or not. My guess is not.
Yes, the receiver works just fine. The RV-4C is on the shelf, not connected.
VOX and ANTI-VOX are set at mid-range.
The transmitter works fine also, I just can't measure the bias current. Can I
assume that the bias current is close to 100 mA if the bias voltage is ~ -60
VDC? It seems like there must be an open in the meter circuit when switched to
set the bias. That should involve switches and relay contacts in the circuit. I
am not very good at tracing circuits on the schematic when they start running
through switches.
In SSB mode, NON-X position, grounding the 'TIP' MIC connector pulls in the
relay.
I should probably order a new relay and try it, but the old one appeared to
work when I had it out and open for cleaning. One set of contacts was somewhat
dirty but I had good continuity after cleaning.
Richard
> Richard -
>
> Probably should have asked this question a while ago, but has this
> transmitter EVER worked, to your knowledge?
>
> Does the receiver work?? Do you have an RV-4(C) connected? Verify that the
> VOX and ANTI-VOX controls on the right side are about mid-range.
>
> Unless something has been rewired, the Cathode line of the PA should read
> that 0.3 to 0.4 VDC ANY time the relay (the four pole one near the power
> connector) is energized, regardless of ANY other switch position. The
> Cathode lead comes through the feedthrough cap on the PA section shield, goes
> to R45 (2 ohms, on the board with the relay) and is hard wired from the other
> end of R45 to the relay contact. This contact is grounded any time the relay
> is energized, grounding the PA Cathodes.
>
> When it's in SSB, in the NON-X position, try grounding the 'TIP' of the MIC
> connector and see if the relay pulls in.
>
> 73, Garey - K4OAH
> Glen Allen, VA
>
> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
> and TR-4/C Service Supplement CDs
> <www.k4oah.com>
>
>
> Donley wrote:
>> Garey,
>> I replaced the 6EV7 and there was no change. The plate voltage on the 6EV7
>> measures a little low at 230 VDC (supposed to 260). This makes the voltage
>> on the relay lower than the 48 VDC (measures about 26 V if I remember
>> correctly, but it seems to pull in okay). I measured the four voltages in
>> all combinations of the sideband switch and the mode switch settings
>> (sideband switch in non-X position and mode switch in SSB position and then
>> in X-CW position). Then (sideband switch in X position and mode switch in
>> SSB position and then X-CW position).
>> The four plate voltage measurements were 687 to 690 VDC.
>> The four screen voltage measurements were 230 to 236 VDC (a little low if
>> 260 is correct).
>> The four grid voltage measurements were around -60 VDC.
>> When the Mode switch was in the SSB position, the cathode voltage was 156
>> VDC for each position of the sideband switch.
>> When the Mode switch was in the X-CW position, the cathode voltage was 0.3
>> to 0.4 VDC.
>>
>> When I said I could adjust the bias voltage in the sideband X position, I
>> didn't tell you that to do that I had to advance the transmitter gain
>> control slightly to get 100 mA. But when I switched back to sideband non-X
>> position, the current dropped to zero with no control by the bias knob on
>> the AC-4.
>>
>> I have pulled the one relay and opened it and cleaned the contacts with no
>> change. Also cleaned the contacts on the second relay.
>>
>> I have a power supply rebuild kit to install but the voltages appear to be
>> okay and steady. I should probably order a new relay and try that.
>>
>> If I adjust the bias pot to get -60 VDC, I have no idea what the bias
>> current is, but I get plenty of power out, around 200 watts, so it seems to
>> work , I just can't measure the current.
>>
>> ??
>> Richard
>>
>>
>> ----- Original Message ----- From: "Garey Barrell" <k4...@mindspring.com>
>> To: "Donley" <donley...@comcast.net>
>> Cc: "Drakelist" <Drakelist@zerobeat.net>
>> Sent: Saturday, July 09, 2011 3:00 PM
>> Subject: Re: [Drakelist] TR-4C Bias Adjustment
>>
>>
>>> Richard -
>>>
>>> I've thought about this some more this afternoon, and I think the next step
>>> is to measure the PA voltages with the switches set per the manual and see
>>> WHAT is missing.
>>>
>>> There aren't that many choices, ONE or more of the three are missing or
>>> incorrect.
>>>
>>> Plate +650 VDC
>>> Screen + 260 VDC
>>> Grid ~ -60 VDC
>>> Cathode ~ 0 VDC
>>>
>>> 73, Garey - K4OAH
>>> Glen Allen, VA
>>>
>>> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
>>> and TR-4/C Service Supplement CDs
>>> <www.k4oah.com>
>>>
>>>
>>> Donley wrote:
>>>> "My guess is that either a KEY is plugged in and open, or the 'shorting'
>>>> jack, isn't! Try just
>>>> inserting a phone plug into the KEY jack several times to see if that
>>>> shorting contact will close as
>>>> it should. Otherwise just insert a shorted phone plug into the KEY jack."
>>>>
>>>> Garey,
>>>>
>>>> Been there, did that. The key is not plugged in but the jack is shorted as
>>>> it should be. When set up according to the manual, there is no bias
>>>> current indicated on the meter when adjusting the bias control, but there
>>>> is adjustable voltage (around -60 VDC +/- adjustable) on the PA grids. If
>>>> I switch the sideband back to the "X" position, there is current indicated
>>>> and I can easily vary it with the bias control and get 100 mA. What is the
>>>> difference in being in the "X" sideband or opposite sideband position?
>>>> Both are done with no transmitter gain and I get current in the "X"
>>>> position and not in the other. Maybe there is an open condition on the
>>>> sideband switch when it is in the non "X" position.
>>>>
>>>> Question - Is the bias current just plate current with no transmitter gain?
>>>>
>>>> Thanks.
>>>> Richard
>>>> kc9ub
>>>>
>>>>
>>>>
>>>>
>>>> ----- Original Message ----- From: "Garey Barrell" <k4...@mindspring.com>
>>>> To: "Donley" <donley...@comcast.net>
>>>> Cc: "Drakelist" <Drakelist@zerobeat.net>
>>>> Sent: Friday, July 08, 2011 11:18 PM
>>>> Subject: Re: [Drakelist] TR-4C Bias Adjustment
>>>>
>>>>
>>>>> Richard -
>>>>>
>>>>> I'm not sure I follow your description below.
>>>>>
>>>>> 1. There is only ONE metering circuit, NO switching involved. If it can
>>>>> read PLATE current it can also read BIAS current.
>>>>>
>>>>> 2. 26 V across the relay sounds low, but if it pulls in that can be left
>>>>> til later.
>>>>>
>>>>> The manual says to switch the SIDEBAND switch counter-clockwise (the
>>>>> 'non-X' position) and the MODE switch to X-CW. I don't have a TR-4C set
>>>>> up at the moment, but I believe the KEY has to be closed. IF you have a
>>>>> key plugged in, it must be shorted. IF you do NOT have a key plugged in,
>>>>> there is a contact on the key jack that is 'supposed' to short the key.
>>>>> IF this contact does not MAKE properly you would see what I think you are
>>>>> describing.
>>>>>
>>>>> The goal here is to put the transceiver into TRANSMIT mode (X-CW) with
>>>>> the 'non' X SIDEBAND selected and the MIC GAIN at minimum. This should
>>>>> register the BIAS current of the PA stage since you're essentially in SSB
>>>>> with no audio applied, resulting in only the suppressed carrier and no
>>>>> PLATE current.
>>>>>
>>>>> My guess is that either a KEY is plugged in and open, or the 'shorting'
>>>>> jack, isn't! Try just inserting a phone plug into the KEY jack several
>>>>> times to see if that shorting contact will close as it should. Otherwise
>>>>> just insert a shorted phone plug into the KEY jack.
>>>>>
>>>>> 73, Garey - K4OAH
>>>>> Glen Allen, VA
>>>>>
>>>>> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
>>>>> and TR-4/C Service Supplement CDs
>>>>> <www.k4oah.com>
>>>>>
>>>>>
>>>>> Donley wrote:
>>>>>> A few weeks ago I started working on putting a TR-4C back on the air. I
>>>>>> posed a question about the bias adjustment. I finally got back to
>>>>>> working on the transceiver and still have some questions. I have
>>>>>> followed all the information that has been sent to other people with
>>>>>> bias problems, but that info has not helped me.
>>>>>> My problem is that the bias current is not displayed or changed on the
>>>>>> Plate Current meter when I adjust the bias control. I can measure and
>>>>>> adjust the bias voltage on the final grids so I know the system is
>>>>>> working, I just can't measure the current. I have done most of the
>>>>>> suggested things: loosen and retighten most ground screws, pulled and
>>>>>> checked all tubes and used Deoxit on the pins and reinserted multiple
>>>>>> times to clean the pins and sockets and cleaned the contacts on the
>>>>>> relays. The 48 volt relay only has 26 volts on the pins, but it appears
>>>>>> to pull in okay and work. Is 26 volts normal?
>>>>>> Using the Drake manual instructions for bias adjust, no plate current
>>>>>> reading is detected even though everything seems to be working. With the
>>>>>> sideband switch in the clockwise position (opposite what the directions
>>>>>> say) and transmitter gain full counterclockwise, I can adjust the plate
>>>>>> current with the bias control. I also get full power output and can
>>>>>> control the plate current with tuning and loading.
>>>>>> It seems everything is fine except being able to measure the bias
>>>>>> current with the recommended setup procedure.
>>>>>> Any suggestions would be appreciated.
>>>>>> 73
>>>>>> Richard
>>>>>> kc9ub
>>>>>
>>>>
>>>>
>>
>>
>
> _______________________________________________
> Drakelist mailing list
> Drakelist@zerobeat.net
> http://mailman.zerobeat.net/mailman/listinfo/drakelist
_______________________________________________
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist
_______________________________________________
Drakelist mailing list
Drakelist@zerobeat.net
http://mailman.zerobeat.net/mailman/listinfo/drakelist
