SZ13C zener replacement for 1964 JMI Vox T60?
Hi all,
New member here, first post!
Recently acquired a 1964 Vox T60 chassis that I feared was headed for the scrap bin. Get the feeling the chassis was unloved for the last 30+ years as it sat on a shelf and was very grimey and dirty.
I get it; not a very reliable amp and thus probably not very desirable. Also not very powerful. It had a lot going against it...
But if I can get this repaired, would probably make a cool little recording amp for bass.
Anyway, the original Arrow power switch plastic bat handle was broken and so was the voltage selector. The front panel was bashed in which may have been the reason for the aforementioned.
But the goal is to save this from the trash.
Did not know if the amp was funcitoning upon arrival as various components in the output section (including the output transistors) were replaced rather amateurishly.
The driver transformer was measured having DC resistances of 32 ohms on the primary with 4.5 ohms on each of the secondaries so I'm presuming that is fine. Power transformer confirmed at 55 VAC on the secondary (27.5VAC CT).
Disassembled down to the chassis. Worked the front panel dent back out (carefully; aluminum chassis!). Straightened the faceplate out, hardwired the PT to mains voltage, new power switch. Replaced all the eletrolytics and a few of the resistors in the output (R23, R27, R30, R31). Will be using silicon PNP MJ15025G for the outputs (of course need to rebias).
I attempted to reuse the original G.E.C. SZ13C zener (stud mount) but the cathode lead broke off inside the body...
I tried to find a datasheet for it, no such luck!
Is it safe to assume that this is essentially a basic 13V 1W zener? If so, would there be a problem using something like a BZX85C13 or 1N4743A?
Some pics before and during the refurb:
And the schematic if anyone's curious:
Hi all,
New member here, first post!
Recently acquired a 1964 Vox T60 chassis that I feared was headed for the scrap bin. Get the feeling the chassis was unloved for the last 30+ years as it sat on a shelf and was very grimey and dirty.
I get it; not a very reliable amp and thus probably not very desirable. Also not very powerful. It had a lot going against it...
But if I can get this repaired, would probably make a cool little recording amp for bass.Anyway, the original Arrow power switch plastic bat handle was broken and so was the voltage selector. The front panel was bashed in which may have been the reason for the aforementioned.
But the goal is to save this from the trash.
Did not know if the amp was funcitoning upon arrival as various components in the output section (including the output transistors) were replaced rather amateurishly.
The driver transformer was measured having DC resistances of 32 ohms on the primary with 4.5 ohms on each of the secondaries so I'm presuming that is fine. Power transformer confirmed at 55 VAC on the secondary (27.5VAC CT).
Disassembled down to the chassis. Worked the front panel dent back out (carefully; aluminum chassis!). Straightened the faceplate out, hardwired the PT to mains voltage, new power switch. Replaced all the eletrolytics and a few of the resistors in the output (R23, R27, R30, R31). Will be using silicon PNP MJ15025G for the outputs (of course need to rebias).
I attempted to reuse the original G.E.C. SZ13C zener (stud mount) but the cathode lead broke off inside the body...
I tried to find a datasheet for it, no such luck!
Is it safe to assume that this is essentially a basic 13V 1W zener? If so, would there be a problem using something like a BZX85C13 or 1N4743A?
Some pics before and during the refurb:
And the schematic if anyone's curious: