Lou W1QJ,
You sir are a Genius! It took me a minute, but I know who you are because I
seem to remember meeting you at the Old Dayton hamvention several years ago.
Its a bit hazy but I seem to remember you having a booth there.
Anyway, To your suggestion, I took a look at the suppressors that I had built
5 or 6 years ago and lo and behold, *the values were wrong on the resistors* ,
additionally I’m not convinced they were of the non-inductive variety. Whoops.
I unsoldered the ones I initially used and replaced them with 2 100ohm 3 watt
non-inductive type, plugged it in, turned it on, keyed it up and BoohYah, 95ma
Idle current in CW mode.
Thank you so much for that hint, this thing has been sitting on my shelf for ~6
years and it always really bothered me that I hadn’t solved the riddle of why
it was pegging the meters like that. Now I can put it in line and use it! If
you come back to Xenia this year, your steak dinner is on me!
Thanks again for your help!!!,
Colin
K8MDX in Grass Lake MI
> On Jan 15, 2019, at 9:41 AM, <gudguyham@aol.com> <gudguyham@aol.com> wrote:
>
> Assuming all your work is correct and there are not shorts in any of the
> transformers, I would have to say that the amp is going into oscillation
> which would lead me to look closely at the parasitic suppressors.
>
>
> -----Original Message-----
> From: Colin Cooper via Amps <amps@contesting.com>
> To: amps <amps@contesting.com>
> Sent: Tue, Jan 15, 2019 9:31 am
> Subject: [Amps] SB-220 Problem has me stumped, looking for some guidance on
> what to look at next
>
> Hello everyone,
> I bought a SB-220 as a project at Hamvention in Ohio, I think I paid about
> 400 dollars for it, It was pretty dirty but complete. I wanted to restore one
> of these to compliment my SB200 that I have already restored.
> The problem:
> When the amp is plugged in and turned on resting at idle, it seems to be
> fine. However when you key the amplifier the Plate and the Grid meters are
> both PEGGED. The meter lights also dim as to indicate that the amp is using
> quite a bit of current.
>
> Things I have changed/updated:
> I Installed the Harbaugh electronics boards, so it has a new cap string as
> well as a new HV and metering board.
> I also installed a new TX/RX relay and the “Soft Key” so that my new radios
> could key the amp without damage.
> I Directly grounded the grids on the tube sockets, removing the mica
> capacitors.
>
> Things I have checked:
> HV: HV is good, the cw/tune / ssb switch works I have 2400 volts in cw and
> 3000 in ssb
> Tubes: I also own two other tl-922 kenwood amps that use the same tubes, so I
> swapped a set of proven good eimac 3-500z’s from one of those amps into this
> one - no change
> 120-vs-220 voltage: it does this regardless of how the input power is
> configured
> The Bias Diode circuit on the harbach board, I triple checked my
> assembly/installation and see no problems
> The 120v Bias/relay Power supply is working.
> The Bias relay: I initially thought this was a bias issue and so I triple
> checked the configuration of the bias circuit. I have also reconfigured the
> bias circuit to resistive bias and there was no change. The grid and plate
> meters still peg when keying the amp.
> The center tap of the filament transformer: It does not appear to be shorted
> to ground.
> The amp acts like something somewhere is shorting to ground but only when the
> amp is Keyed up.
>
>
> I would really really appreciate any help or guidance that the group could
> provide on what to look at next.
>
> Thank you and 73
> Colin Cooper
> K8MDX, Grass lake Michigan
>
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