[Boatanchors] SB-610 monitor scope technical assist

[Phil]

I don't have one, or the schematic, but 2700 Ohms (2.7K) seems to be 
mighty low for a grid circuit and could account for the low gain. Are 
you sure that it shouldn't be 270K or 27K?


-- 
73 de Phil,  KO6BB
http://ko6bb1.multiply.com/ (OTR Blog)
http://www.qsl.net/ko6bb/  (Web Page)

RADIOS:
Grundigs: Satellit 750 (2011), S-350 (2006)&  G6 (2011).
Radio Shack: DX-380 digital portable (circa 1990).
Yaesu: Two FT-8800 Mobiles, VX8R Quad-Band (circa 2010).
Zenith: Royal-7000 Transoceanic (circa 1969).

ACCESSORIES: MFJ 1040C Pre-Selector, W9GR Audio DSP.
ANTENNA: PAR 60 Foot End-Fed, up about 28 feet at Apex.

Central California


On 11/18/2011 11:24 PM, Dick KF4NS wrote:
> Hi Guys,
> First I will give you a short history. I bought  it used in Dec. 2002 and immediately replaced the CRT
> with the flat screen 3RP1, and the HV caps, diodes and resistors as well as the 600v supply caps. Since
> then, replaced several high value resistors out of tolerance. Transformer secondary voltages are right
> on.
>
> I have not replaced the can caps yet but will soon because voltages are low.
>
> The trouble is with the vertical amp,  V2 tests fine. It has had very low gain from the beginning.  All
> resistors are new in vert. circuit and caps test good now. It is set up for 3395khz and has the correct
> caps. There is no loss between the rear vert. IN jack and the wiper terminal of vert. gain pot. After
> that I lose 300mv at the control grid with 500mv (rms spec for 3395) at 3395khz unmodulated injected from
> my sig gen to the IN jack and read at the control grid with my TEK scope, The 2700ohm grid resistor is
> new. Vertical pot is good and set for max. No sense in testing the CRT voltages until all the
> electrolytics are replaced.
> I tried tweaking the slug for L1 and see no change at the grid. QUESTION: are the input/output tuned
> circuits similar to the TPTG circuits for oscillators? There is no mention of test procedures for the
> tuned circuits or the values for the coils.
>
> I am sure I have left something out so please excuse me and tell me what is missing. Oh, yes, I don't get
> the 5Mohm at lug 2 strip B, actually it is only a bit more than 2Mohm. Followed the troubleshooting guide
> to no avail.
>
> Any advice will be greatly appreciated.
> Thanks and 73, Dick KF4NS
> St Petersburg, FL 33714 USA
> Keep The Glow!
>
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