Thats to everyone who responded, Lou W1QJ pointed me in the right direction and
its working correctly now. It was the parasitic suppressors!
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.
Thanks again everyone!
-Colin
K8MDX
> On Jan 14, 2019, at 3:21 PM, Colin Cooper <evinruding@yahoo.com> wrote:
>
> 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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