[Heathkit] RE: SB-610?

[ehertz]

Hi again everyone! I found a major problem! (This is getting to be fun) Someone had swapped the PECs! So I put the right PEC on the right side of V4 and voila! I now have single tone and dual tone.! In the meanwhile until I discovered that I replaced the 220K for a 270K and also swapped out a 10uF bypass cap. Neither of which proved bad, but oh well.

Now the big and final (hopefully) question!

Now that the oscillators work...How do I tune them? Instead of 1500 Hz and 1950 Hz, I have 1625 and 2047 Hz.

Can anyone tell me what component I could add at what point to bring these down? I am hoping that a well-placed capacitor or two somewhere would help me get closer to the right numbers.

Thanks again to everyone on the list. I got many replies off-list, all were very helpful to me in narrowing down the problem (often by suggesting things to try that ended up not being the problem, but helped me eliminate potential sources of the problem--allowing me to focus on the remaining parts of the circuit until I found it!)

Eugene



>On Mon, 19 Feb 2007 19:09:30 +0000 "ehertz" <ehertz at tcaf.org> writes: 
>> Hello all! 
>> 
>> Update on the 610 single tone output. Through careful and time 
>> consuming tracing, I located one faulty soldering joint. The join 
>> allowed B+ to get to the plate of V4B but not V4A! I was very luck 
>> and thrilled to have located this fault. I resoldered and things are 
>> slightly improved... 
>> 
>> Now, while watching the tone output on a scope: When I go from "off" 
>> to "1.5 KHz tone" I see a *momentary* sinewave on the scope. It then 
>> seems to fade to zero in about 1/2 second or less. Every time I go 
>> from off to 1.5 I see that momentary sinewave. 
>> 
>> So it seems the signal may be being dampened out and continuous 
>> oscillation is not occurring. So I kept looking... 
>> 
>> I believe I located an incorrect component value. Seems the 
>> resistor from the first grid of V4A (pin 5) is supposed to be 270K. 
>> On my unit, it appears to be 220K. Can anyone confirm that this 
>> could in fact be preventing this from oscillating? If the answer is 
>> no, I'd rather keep looking and leave that there. Its really burried 
>> under a ton of other components. 
>> 
>> Any insight appreciated. thanks! 
>> Eugene 
>> 
>>