[Amps] Fwd: Re: SB-220 Bias Issue, Too High of Plate Voltage?

[Jim]

MOST of the Harbach stuff is safe, but costs at least twice what it 
should. Stay away from the Nichrome parasitic suppressors (too much L, 
that makes 'em run WAY hot on 28 MHz). Rebuild your using Globar (WAY 
expensive) or NOS carbon composition resistors. Ebay seller 
'bigsmythe74' has 56/10%/2W for $1/each plus $4/order. See #400880759592 
<http://www.ebay.com/itm/400880759592>.

In the HV meter multiplier string, Heathkit used three 4M7/1W carbon 
composition resistors to TRY to make 'em last (it didn't work). CC 
resistors absorb moisture ('cuz they're not sealed), and then soar in 
value. It's more noticeable in high nominal value resistors. Later 
aftermarket SB-22x rectifier/meter boards substituted fourteen 1M0 Metal 
Film resistors. The easiest/cheapest thing to do is upgrade the OE PCB. 
I replaced R6/R7/R9 with 4M7/1W/5% "Metal Glaze" resistors (Vishay 
pn VR68000004704JAC00). The datasheet (*link* 
<http://www.vishay.com/docs/28907/vr25vr37vr68.pdf>) sez they're OK to 
10KV. Digi-Key stocks 'em for $0.78 each. The rectifiers are kinda wimpy 
and should be upgraded to 1N5408 (3A/1KV). Order an extra rectifier to 
add between -HV and chassis for meter protection. Tom W8JI shows how 
here (*link* <http://www.w8ji.com/metering_amplifier.htm>).

The electrolytic capacitors in the HV supply can be changed to CDE 
381LR-series. If you stay below about 300uF, a step-start circuit 
(Harbach "Soft Start") isn't needed. Everyone sells 'em for about 
$6/each (to fit the OE plastic holder, you want 35mm OD). Replace the 
30Ω/7W wirewound resistors w/ 100KΩ/3W Metal Oxide types. Your HV filter 
capacitors will like less heat.

I like Jim W7RY's "QSK" circuit. It drives FAST vacuum/reed relays that 
eliminate hot-switching when using VOX (fone) or semi/full break-in 
(Morse). You also get a relay driver (Harbach "Soft Key"), adjustable 
operating bias, relay contacts that will never oxidize, and dead quiet 
operation.

The cooling fan from Grainger is Dayton pn 4M070 (*link* 
<http://www.grainger.com/product/DAYTON-1-150-HP-C-Frame-Motor-4M070>)... 
for over twice the cost from Harbach ($50). For the extra cost, Harbach 
supplies a fan blade.

vy 73,
Bryan WA7PRC


On Saturday, May 18, 2019, 5:54:30 PM PDT, Jim <jimw7ry at gmail.com> wrote:

Sorry for not changing the subject.

If that is the true voltage, and you had to add that many diodes, then 
you have another problem.

An oscillation or parasitic of some sort.  Better measure the voltage 
with an accurate meter or check your multiplier resistors in your high 
voltage metering circuit.

Thanks 73 Jim W7RY

On 5/18/2019 6:56 PM, Joe wrote:
> Only relying on the Meter on the amp, do not have a volt meter that 
> goes that high.
>
> But 3500+ a smidgen, maybe 3600
>
> On 5/18/2019 6:51 PM, Jim wrote:
>> What is your MEASURED plate voltage?
>> Thanks 73 Jim W7RY
>> On 5/18/2019 6:11 PM, Joe wrote:
>>> This AMP had it before and ran sooo cool it was wonderful.
>>>
>>> Now with the new transformer I literally had to double the amount of 
>>> diodes to ger the idle low enough so ever with ZERO WAYYS Drive I 
>>> mean no watts at all put it in transmit mode and the plates 5 
>>> seconds later would be the color of an orange!
>>>
>>> Finally when I got the idle current down to 120 or so at least with 
>>> no power the plates stay gray. be even a medium length CQ, like say 
>>> CQ CQ CQ CQ CQ CQ DE WB9SBD WB9SBD K
>>>
>>> We are again bright orange.
>>>
>>> Joe WB9SBD
>>>
>>> On 5/18/2019 5:45 PM, Jim wrote:
>>>> Why do you think you need such a thing Joe?
>>>> Thanks 73 Jim W7RY
>>>> On 5/16/2019 11:23 PM, Joe wrote:
>>>>> Has anyone installed one of these into their SB-220?
>>>>>
>>>>> http://www.ameritron.com/Product.php?productid=EBS-1H
>>>>>
>>>>> Joe WB9SBD
>>>>>
>>>>> On 5/10/2019 7:55 PM, Jim wrote:
>>>>>> I tried to post a schematic and the moderator wont allow it for 
>>>>>> some unknown reason.
>>>>>>
>>>>>> Schematic is attached.
>>>>>>
>>>>>>
>>>>>> Thanks
>>>>>> 73
>>>>>> Jim W7RY
>>>>>>
>>>>>> On 5/10/2019 9:52 AM, Lou Everett, Sr. wrote:
>>>>>>> Where is it?
>>>>>>>
>>>>>>> Lou WA5LOU
>>>>>>>
>>>>>>> On Fri, May 10, 2019 at 7:41 AM Jim <jimw7ry at gmail.com 
>>>>>>> <mailto:jimw7ry at gmail.com> <mailto:jimw7ry at gmail.com> 
>>>>>>> <mailto:jimw7ry at gmail.com>> wrote:
>>>>>>>
>>>>>>>     Here is the modification (simple schematic) to the cut-off 
>>>>>>> bias in
>>>>>>>     the
>>>>>>>     Kenwood TL-922 amplifier.
>>>>>>>
>>>>>>>
>>>>>>>     --     Thanks
>>>>>>>     73
>>>>>>>     Jim W7RY