I swapped V4 with a NOS 12BE6. It made no difference to the s-meter.
Thanks for the clarifications on the resistances around V3. My 2-C is #2804, well past the changes made at #1000.
I measured the DC voltage at C48: 10.1v. Seems very low.
Tom
On 10/12/06, Garey Barrell <
[EMAIL PROTECTED]> wrote:
Tom -
OK. Next try V4. It, and V1 are controlled by the AGC #2 and are the
"other side" of the S-Meter bridge.
Your readings on V3 (I'm assuming you're referring to Pin 2, not Pin 3)
reflect a circuit change. There are at least two versions of the 2-C
that I'm familiar with, and the voltage/resistance charts weren't
updated to reflect the later version. Version 2 started at s/n 1000.
Your readings are correct for Version 2 units.
The AF collector voltage seems too low. A leaky Q6 can cause this.
What is the voltage at the top of C48? (The +12V power supply filter cap)
73, Garey - K4OAH
Atlanta
Drake 2-B, 4-B & C-Line Service CDs
<www.k4oah.com>
Tom Taylor wrote:
> I tried swapping several 12BA6's (V5) at Garey's suggestion. All
> caused me to recalibrate the s-meter zero and I was able to get -13v
> at tp-1, but the s-meter is nearly unreponsive. It'll register S4 on
> only the very strongest of signals. I replaced the 12BZ6 with a NOS
> tube and that had no positive effect on the s-meter either.
>
> I did a voltage and resistance check against the table in the manual
> just to see if there was anything way off. Surprisingly, the case of
> the output transistor was at 10.3v instead of 12.5v. Perhaps that's
> why audio isn't ear blasting. I'll have to investigate further. As far
> as the resistance checks, everything was within reason for a 35 year
> old (perhaps older) radio, except for the resistances around V3, the
> mixer and VFO. Pin 3 is supposed to be 330 ohms and I measure .6 ohms.
> Pin 7 is supposed to be 7k and I measure 1m. Should I believe the
> chart in the manual? The VFO certainly seems to work fine. With those
> measurements so far off, I wouldn't expect the receiver to be so
> operational, except for the S-meter.
>
> I guess I'll dive deeper and try and understand why those couple
> resistance measurements are so far from what's listed in the chart.
>
> Tom n7tm
>
>
