Garey,
Thanks for the clarification. As always, you are the source!
As for the floating K, I think it's normal when the mode switch is in the SSB
position and the PTT is not pressed. I know you wanted Richard to measure the
voltage during TX, but I think he measured it while not transmitting (i.e. ptt
not pressed). To me the problem seems that the final tubes stays cutoff
within the bias voltage range provided by the AC-4. I thought it was the screen
voltage issue, but again I am relatively new to this hollow state technology so
it was just a guess.
Kihwal, K9SUL
________________________________
From: Garey Barrell <k4...@mindspring.com>
To: drakelist <Drakelist@zerobeat.net>
Sent: Tuesday, July 12, 2011 12:57 PM
Subject: Re: [Drakelist] TR-4C Bias Adjustment
Kihwal -
I agree with most of what you said. The Screen voltage is slightly low, most
likely as a result of leakage in the AC-4 filter caps. But I do NOT believe it
has any significant effect on this problem as he is able to get full power in
the X-CW position.
You are correct on the X-CW shifting the Carrier Osc (via relay K2) so that the
CARRIER signal will go through one of the filters. This configuration is used
for both tune-up and CW operation. The SIDETONE is NOT used for this purpose
in the TR-4C, only to operate the VOX circuit.
In the T-4XC, the CO is shifted for CW operation. However, in TUNE mode the
SIDETONE IS applied to the Balanced Modulator, generating a single tone SSB
signal, and the CO is NOT shifted.
The key here is that these Cathodes are NOT grounded in either SSB position. I
believe that is the result of the PTT/VOX circuit NOT pulling in the relay in
that switch position. Grounding the tip of the MIC connector causes the relay
to pull in, and I believe that will cause the PA Cathodes to read the correct
near zero reading rather than the 156 VDC he measured. The PLATE meter should
then read correctly. We'll see! :-)
I'm now thinking the problem is in the VOX circuitry.
73, Garey - K4OAH
Glen Allen, VA
Kihwal Lee wrote:
> 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
> >> <mailto:k4...@mindspring.com>>
> >> To: "Donley" <donley...@comcast.net <mailto:donley...@comcast.net>>
> >> Cc: "Drakelist" <Drakelist@zerobeat.net <mailto: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
> >>>> <mailto:k4...@mindspring.com>>
> >>>> To: "Donley" <donley...@comcast.net <mailto:donley...@comcast.net>>
> >>>> Cc: "Drakelist" <Drakelist@zerobeat.net <mailto: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
> >>>>>
> >>>>
> >>>>
> >>
> >>
> >
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