We have a Hastings VT-4B made by Beede Electronic Instruments Co,
Inc. The line transformer in this unit has burned. It's a custom
transformer, made by Regional Mfg. Specialists, part number 528214-G.
From what I can tell, it just feeds into a bridge, center tap
grounded, which powers the LM78L12 & L79L12 regulators. Dimentions on
it are 1.635in x 1.325in x 1.325in. It has wire leads, no terminals,
and is mounted by two screws through the cores. Any suggestions for
replacement? Would a 12.6-0-12.6 transformer give enough headroom for
the regulators?

Thanks,
Steve

sck0006 writes:

We have a Hastings VT-4B made by Beede Electronic Instruments Co,
Inc. The line transformer in this unit has burned. It's a custom
transformer, made by Regional Mfg. Specialists, part number 528214-G.
From what I can tell, it just feeds into a bridge, center tap
grounded, which powers the LM78L12 & L79L12 regulators. Dimentions on
it are 1.635in x 1.325in x 1.325in. It has wire leads, no terminals,
and is mounted by two screws through the cores. Any suggestions for
replacement? Would a 12.6-0-12.6 transformer give enough headroom for
the regulators?

The electroncs draw very little power so it might be OK. 12.6 * 1.4 (peak) is
about 17.6 V, But, you need 1.4 V or so for the bridge, another 2? V for the
regulator, and something for ripple, so that's getting close to the required
12 VDC output, especially over the allowed line voltage range.

I'd probably go with 14 VRMS or so if there is a standard part you can fit
in there.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
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On 17 Dec 2007 19:03:11 -0500, Sam Goldwasser
wrote:

sck0006 writes:

We have a Hastings VT-4B made by Beede Electronic Instruments Co,
Inc. The line transformer in this unit has burned. It's a custom
transformer, made by Regional Mfg. Specialists, part number 528214-G.
From what I can tell, it just feeds into a bridge, center tap
grounded, which powers the LM78L12 & L79L12 regulators. Dimentions on
it are 1.635in x 1.325in x 1.325in. It has wire leads, no terminals,
and is mounted by two screws through the cores. Any suggestions for
replacement? Would a 12.6-0-12.6 transformer give enough headroom for
the regulators?

The electroncs draw very little power so it might be OK. 12.6 * 1.4 (peak) is
about 17.6 V, But, you need 1.4 V or so for the bridge, another 2? V for the
regulator, and something for ripple, so that's getting close to the required
12 VDC output, especially over the allowed line voltage range.

I'd probably go with 14 VRMS or so if there is a standard part you can fit
in there.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
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Thanks for the reply Sam, always apprecaited. The only thing I could
find with the right dimensions in a hurry was a Hammond 266C24. I
guess we'll just wait unitl it gets here and see. I believe I'm going
to have to rip off the chassis mount part and drill through the cores,
but maybe I'll get a little lucky.

Thanks again,
Steve

Steve writes:

On 17 Dec 2007 19:03:11 -0500, Sam Goldwasser
wrote:

sck0006 writes:

We have a Hastings VT-4B made by Beede Electronic Instruments Co,
Inc. The line transformer in this unit has burned. It's a custom
transformer, made by Regional Mfg. Specialists, part number 528214-G.
From what I can tell, it just feeds into a bridge, center tap
grounded, which powers the LM78L12 & L79L12 regulators. Dimentions on
it are 1.635in x 1.325in x 1.325in. It has wire leads, no terminals,
and is mounted by two screws through the cores. Any suggestions for
replacement? Would a 12.6-0-12.6 transformer give enough headroom for
the regulators?

The electroncs draw very little power so it might be OK. 12.6 * 1.4 (peak) is
about 17.6 V, But, you need 1.4 V or so for the bridge, another 2? V for the
regulator, and something for ripple, so that's getting close to the required
12 VDC output, especially over the allowed line voltage range.

I'd probably go with 14 VRMS or so if there is a standard part you can fit
in there.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/

Thanks for the reply Sam, always apprecaited. The only thing I could
find with the right dimensions in a hurry was a Hammond 266C24. I
guess we'll just wait unitl it gets here and see. I believe I'm going
to have to rip off the chassis mount part and drill through the cores,
but maybe I'll get a little lucky.

Don't drill anything. Use hot melt glue or nylon ties to secure it.

If it turns out to be marginal, maybe replace the regulator with a low
dropout equivalent.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
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Ok, we got the transformer in, physically it is smaller than the
other, mounting it shouldn't be a problem. Without a vacuum tube
plugged in, the regulators maintain regulation down to 100VAC line
voltage. Now I want to load it to make sure it does in fact have
enough headroom and that the transformer won't overheat. What sort of
load do these tubes impose on the circuit?

Thanks,
Steve

Steve writes:

Ok, we got the transformer in, physically it is smaller than the
other, mounting it shouldn't be a problem. Without a vacuum tube
plugged in, the regulators maintain regulation down to 100VAC line
voltage. Now I want to load it to make sure it does in fact have
enough headroom and that the transformer won't overheat. What sort of
load do these tubes impose on the circuit?

Not much. For the DV-4D tube used with the VT-4, the heater current is
29 mA at 320 mV, about 9 mW. So put a 10 ohm resistor between pins
3 and 5 of the octal socket but the power supply won't even notice.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
| Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
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On Dec 23, 6:32*pm, Sam Goldwasser wrote:
Steve writes:
Ok, we got thetransformerin, physically it is smaller than the
other, mounting it shouldn't be a problem. *Without a vacuum tube
plugged in, the regulators maintain regulation down to 100VAC line
voltage. *Now I want to load it to make sure it does in fact have
enough headroom and that thetransformerwon't overheat. *What sort of
load do these tubes impose on the circuit? *

Not much. *For the DV-4D tube used with the VT-4, the heater current is
29 mA at 320 mV, about 9 mW. *So put a 10 ohm resistor between pins
3 and 5 of the octal socket but the power supply won't even notice.

--- sam | Sci.Electronics.Repair FAQ:http://www.repairfaq.org/
*Repair | Main Table of Contents:http://www.repairfaq.org/REPAIR/
+Lasers | Sam's Laser FAQ:http://www.repairfaq.org/sam/lasersam.htm
* * * * | Mirror Sites:http://www.repairfaq.org/REPAIR/F_mirror.html

Important: Anything sent to the email address in the message header above is
ignored unless my full name AND either lasers or electronics is included in the
subject line. *Or, you can contact me via the Feedback Form in the FAQs.

I guess it's just the light load on the transformer, but a little
12-0-12VCT transformer rated at .085A has no problem giving the
regulators plenty of extra room. At 105VAC line voltage with the
circuit loaded, the filter caps have ~16VDC on them, plenty of room
for a 12V regulator. There is only ~20mA draw on each leg of the
transformer, so it should be happy.
Thanks for the help,
Steve