开云体育

Years ago, a PA system amplifier that had been donated to us for hamfest use had an annoying hum when we checked it out before its first hamfest use. Nothing I tried would “fix” the hum. Until ---

I recapped my Swan 270B about 21 years ago and its been my most modern HF rig since. When I use a nice old set of headphones, there is no hum. But a modern set of high fidelity phones introduces

Jim Re:: “The Bass IN/OUT thing could be attributed to the change in gain of the 1st audio amp. Figure 11, the audio filter curve, shows that the gain is 100+X higher when the bass switch is in the

Jacques, I “may” guilty of not returning caps to the same ground as original………… I need to look into this. I took lots of before and after pics so I should be able to confirm Tom Sent:

Ok, made a couple videos, excuse the camera work and narrating………. https://drive.google.com/file/d/10rFu1-W59o6I1Ro8Q4Lq0jG9HbNen6Dt/view?usp=sharing

I don’t know Jim, I have several other radios (too many actually…) of this vintage that don’t have this hum. Yes I neglected to address the speaker, sorry. My bench setup uses an older

Jacques, I was going thru your recent post and started turning into a pretzel; adding and then removing a resistor. See my “side-by-each” . 180 “M?” but no squiggle Sent: Tuesday, February

Tom and JacquesYou are overlooking an alternative, that nothing is actually wrong.? AFAIK. the radio works well but there is a noticeable hum.? Hum is subjective, if you have listened to solid state

Let’s resume the case : Tom pulled the 6SC7 and the “hum” remained. He shorted the two 6V6 grids to GND and the hum disappeared. No hum when the “bass” switch is in the IN position (both

Gents, dunno about all that, but why the no hum in the In position? And when base is boosted? _,_

RichardI was a bit clumsily in my previous attempt so I will try again.?? All aluminum electrolytic capacitors are self resonate.? ?There is a frequency where the capacitor becomes an inductor.?

Yes, wiring is as shown on schematic Yes bass "in" boost the bass response.

Tom, move some stuff and things change… no cold solder joints around there? Sent: Monday, February 17, 2025 8:59 PM To: [email protected] Subject: Re: [HallicraftersRadios] SX-28A Hum

Please confirm: 1, the wiring is actually as shown on the diagram. 2, the bass boost is present with the switch in the IN position. If so I am thoroughly puzzled. If the hum is 60Hz I wonder if

Time to re-evaluate where I’m at and what I’ve tried, yes the hum is still there……. Tried three different 6SC7’s no noticeable difference between each one. Confirmed the wiring of the switch

Richard and Jim, I got caught on the top paragraphs, and did not go thru it all.. but…!!! As I have seen it, at 10mfd, C44 is hopefully holding the “reduced B+” steady for both parts of the

Emanuele, very good that you did all this, you can let your brain cool off now nor a bit. First, do you have any idea if this is an early run, or a later one?. See what is in red first! Richard

Greetings to the group: I see I will have to go back and duplicate Emanuele's measurement setup exactly; I can do that but it will take a while. In the mean time, I have taken some more pictures with

Sweep of MIX tanks: Setup is the same as ANT but the injection point is V1pin8 and the probing point is V2pin8. The signal in band 1 is very low (effect of lack of coupling between V1 and v2). I had

I suppose I have to reply to each comment. The plate load is the impedance in the plate circuit between supply voltage and plate, that develops the signal output. In the half of the 6SC7 that the bass