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T-4XC diode CR1 question

 

This diode (Z-13B) is listed as a voltage regulator. The voltage I am seeing across this diode is only +1.2 volts, which seems unusually low. I don't recall ever seeing a Zener diode that goes below 3 volts. Searching the Internet, I couldn't find any info on this part. Is this the correct voltage for this part? If not, what should it be?
--
Bill N0CU
 

Bill:

You should see about 13 VDC on that zener.? It's a 13V 1 watt zener.? Check the adjacent tantalum cap, C191.? I have seen these go bad...and take the zener with it!? Chirpy CW is sometimes the clue.

73
Peter
VE7PS

On Wed, Mar 8, 2023 at 10:11?AM Bill Leonard N0CU <billincolo73@...> wrote:
This diode (Z-13B) is listed as a voltage regulator. The voltage I am seeing across this diode is only +1.2 volts, which seems unusually low. I don't recall ever seeing a Zener diode that goes below 3 volts. Searching the Internet, I couldn't find any info on this part. Is this the correct voltage for this part? If not, what should it be?
--
Bill N0CU

 

Bill,

In an older manual CR1 is listed as a Z-13B which is a 13V, 0.5W Zener. In a later manual I see CR1 listed as 1N4743A, 13V, W.

CR1 is the?voltage regulator for the carrier oscillator. It is fed via R7, a 5K, 20W resistor from the?+250VDC bus. If you are only?seeing?
+1.2V then I would look at R7 as well at the?+250V bus.

?image.png

Ken
WA2LBI




On Wed, Mar 8, 2023 at 1:11?PM Bill Leonard N0CU <billincolo73@...> wrote:
This diode (Z-13B) is listed as a voltage regulator. The voltage I am seeing across this diode is only +1.2 volts, which seems unusually low. I don't recall ever seeing a Zener diode that goes below 3 volts. Searching the Internet, I couldn't find any info on this part. Is this the correct voltage for this part? If not, what should it be?
--
Bill N0CU

 

Peter,
I was suspecting from the diode part number that it was probably a 13V device. Is C191 a tantalum? My read on the schematic is that it is one of the two electrolytics in the nearby can.

On Wed, Mar 8, 2023 at 11:44?AM VE7PS <ve7ps@...> wrote:
Bill:

You should see about 13 VDC on that zener.? It's a 13V 1 watt zener.? Check the adjacent tantalum cap, C191.? I have seen these go bad...and take the zener with it!? Chirpy CW is sometimes the clue.

73
Peter
VE7PS

On Wed, Mar 8, 2023 at 10:11?AM Bill Leonard N0CU <billincolo73@...> wrote:
This diode (Z-13B) is listed as a voltage regulator. The voltage I am seeing across this diode is only +1.2 volts, which seems unusually low. I don't recall ever seeing a Zener diode that goes below 3 volts. Searching the Internet, I couldn't find any info on this part. Is this the correct voltage for this part? If not, what should it be?
--
Bill N0CU

 

Bill:

C191 is the tantalum cap adjacent to CR1.? ?See pic from K4OAH's service manual.? And Ken's suggestion about ensuring the +250VDC line and R7 is OK is also good advice.? My bet is on the zener/tantalum though, depending on other symptoms.? Are you getting any power out of the rig at all?

73
Peter
VE7PS

image.png


On Wed, Mar 8, 2023 at 10:59?AM Bill Leonard N0CU <billincolo73@...> wrote:
Peter,
I was suspecting from the diode part number that it was probably a 13V device. Is C191 a tantalum? My read on the schematic is that it is one of the two electrolytics in the nearby can.

On Wed, Mar 8, 2023 at 11:44?AM VE7PS <ve7ps@...> wrote:
Bill:

You should see about 13 VDC on that zener.? It's a 13V 1 watt zener.? Check the adjacent tantalum cap, C191.? I have seen these go bad...and take the zener with it!? Chirpy CW is sometimes the clue.

73
Peter
VE7PS

On Wed, Mar 8, 2023 at 10:11?AM Bill Leonard N0CU <billincolo73@...> wrote:
This diode (Z-13B) is listed as a voltage regulator. The voltage I am seeing across this diode is only +1.2 volts, which seems unusually low. I don't recall ever seeing a Zener diode that goes below 3 volts. Searching the Internet, I couldn't find any info on this part. Is this the correct voltage for this part? If not, what should it be?
--
Bill N0CU

 

Thanks Ken & Peter. Very helpful. The Tx seems to be operating ok- over 120 W out and no observed anomalies. It looks like it is time for me to order K4OAH's manual!
--
Bill N0CU
 

Bill;

You won't regret purchasing the appropriate K4OAH documents for your Drakes.? They sure make it easier to find components.? They aren't perfect....there is no way Garey could cover detailed parts locations?for all versions of radios such as the R-4C, which had several major upgrades.? That said, he did include the various versions of the schematics wherever/whenever he could get them.

If you are seeing 120w out then the?+250 VDC line must be working fine.? Any slight chirp on the CW signal???

73
Peter
VE7PS

On Wed, Mar 8, 2023 at 12:57?PM Bill Leonard N0CU <billincolo73@...> wrote:
Thanks Ken & Peter. Very helpful. The Tx seems to be operating ok- over 120 W out and no observed anomalies. It looks like it is time for me to order K4OAH's manual!
--
Bill N0CU

 

Peter, without K4OAH's info I wrongly concluded that the 10uF electrolytic cap in the can was the one across CR1. With the help of your info I was able to verify that CR1 has the correct 13V across it and that the 1.3 V across the 10 uF electrolytic (C98) is also correct. As an old semiconductor guy, I am on the steep part of the learning curve for tube equipment. I have ordered the K4OAH CD. Thanks again.
--
Bill N0CU
 

Glad you got that?sorted out Bill.? Being one of the first recipients?of Garey's "CD's", I have long been a promoter of his work.? Just wish he'd had more time to finish off all the ones he wanted?to get done.? But he certainly got to most of them.

73
Peter
VE7PS

On Wed, Mar 8, 2023 at 2:32?PM Bill Leonard N0CU <billincolo73@...> wrote:
Peter, without K4OAH's info I wrongly concluded that the 10uF electrolytic cap in the can was the one across CR1. With the help of your info I was able to verify that CR1 has the correct 13V across it and that the 1.3 V across the 10 uF electrolytic (C98) is also correct. As an old semiconductor guy, I am on the steep part of the learning curve for tube equipment. I have ordered the K4OAH CD. Thanks again.
--
Bill N0CU

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