[Amps] Alpha 86

[Paul Christensen]

Drifting off topic but the 86 PIN diode failures can be avoided with correct sequencing and high bias voltage on the Rx diodes. In the last generation of Alpha 87A and 89 amps, I believe the Zener bias string reaches 900V, or close to it.

The second issue is IMD.  Have a look at QST's product review of the Alpha 86 and you'll see the telltale sign that the Tx diodes are not going far enough into conduction.   Easily solved without requiring vaccum relays.  

Glenn would know for sure, but I'm guessing he's seen relatively few PIN diode failures with late-generation (post 1999-2000) Alpha 87A and 89 amps.  The Elecraft KPA1500 and RF-KIT amps both utilize PIN diode T/R switching and I've not heard of any mass casualties to date.

Paul, W9AC

-----Original Message-----
From: Amps <amps-bounces at contesting.com> On Behalf Of David Tenenbaum
Sent: Wednesday, November 9, 2022 9:53 AM
To: Larry Dighera <LDighera at att.net>
Cc: amps at contesting.com
Subject: Re: [Amps] Alpha 86

It was!

Also, as others have said, the 86 was not remotely standardized, with at least 3 different control boards. Mine had blown PIN diodes and I could not find a source, so I built in vacuum relays but it took a lot of probing my control board to find a place to get a control signal for the relays. Not much info on the internet either.

Appreciate all the help from everyone! Awaiting new fuses.

David 

> On Nov 9, 2022, at 9:40 AM, Larry Dighera <LDighera at att.net> wrote:
> 
> 
> I'll bet the fuse that appeared visually intact was 1A not 1.5A. 
> 
> Larry
> WB6BBB
> 
> 
> On Tue, 8 Nov 2022 17:05:47 -0500, David Tenenbaum <dmt013 at gmail.com> wrote:
> 
>> I think you have nailed it Chris: I had initially visually checked the slow blow fuses and they looked fine, but an ohmmeter confirms one is not conductive. My bad for not checking it with a meter first time around. Embarrassing!
>> 
>> Two followups:
>> 
>> 1) The schematic says 1.5 amp slow blow, but the chassis stencil says 1.0 amp SB. I am guessing it should not matter too much which I go with?
>> 
>> 2) Should I be looking at an underlying root cause before trying it with new fuse? I guess worse that can happen is it blows again....
>> 
>> Thanks for the help, sorry for the rookie oversight!
>> 
>> David
>> N1RO
>> 
>> 
>> 
>> 
>>> On Nov 8, 2022, at 4:52 PM, c miller <c_miller_1 at hotmail.com> wrote:
>>> 
>>> Not too odd really.  On 120v it is possible to run the initial startup cycle on just one of the two windings.  Then once the soft start circuit bypasses then both windings come into operation and unit preforms as intended.  However, with either fuse F3 or F4, or resistor R6 or R7, in the soft start circuit being open, no power ever gets passed on to the transformer thus locking the rig in a power off state.  The relay k11 (click) is the only part that is able to operate in that failure mode
>>> 
>>> Chris
>>> VE3CEA 
>>> 
>>> 
>>> Sent from my iPhone
>>> 
>>>> On Nov 8, 2022, at 16:31, gudguyham--- via Amps <amps at contesting.com> wrote:
>>>> 
>>>> ?It’s odd that it works on 120 and not 240.  I looked in the manual but the terminal strip is not numbered on the schematic.
>>>> 
>>>> 
>>>> Sent from the all new AOL app for iOS
>>>> 
>>>> 
>>>> On Tuesday, November 8, 2022, 3:24 PM, David Tenenbaum <dmt013 at gmail.com> wrote:
>>>> 
>>>> Thanks for the feedback!
>>>> I am still on the clock at work but took a break to check R8 and I am seeing 3.98K ohms, so the 4k resistor seems intact. Later tonight when finally done with work I will tear into it to look at the fuses and other resistors, confirm there is REALLY 220 v getting to the unit, and anything else that comes up.
>>>> Thanks all for the ideas!!!!
>>>> David N1RO/VE3TMK
>>>> 
>>>> 
>>>> On Nov 8, 2022, at 2:33 PM, gudguyham at aol.com wrote:
>>>> Did you check R8 for open?
>>>> 
>>>> 
>>>> Sent from the all new AOL app for iOS
>>>> 
>>>> 
>>>> On Tuesday, November 8, 2022, 2:20 PM, David Tenenbaum <dmt013 at gmail.com> wrote:
>>>> 
>>>> Hi All,
>>>> 
>>>> I have an Alpha 86 that I have been using set up for 110v, and finally have access to 220v, so looking forward to seeing what it can REALLY put out. Unfortunately I have made the jumper changes (terminal in the back for 110 operation has locations 1&2 jumpered, 3&4 jumpered, and 5&6 jumpered, but for 220 only locations 2&3 are jumpered), and the unit fails to light up or come online. I hear a single relay activation when I hit the "On" switch, but no lights or fan.
>>>> 
>>>> Fearing I hurt the unit I restored it to 110v operation and all is good. I set it back to 220v and same problem. I checked continuity from the plug's ground to chassis ground, and the hot leads show continuity to the right places. I have been using a 220v SB200 on that outlet just fine.
>>>> 
>>>> Any thoughts or leads appreciated! Never thought I would have a problem just switching supply voltages.....Scan of schematic attached....
>>>> 
>>>> Best,
>>>> 
>>>> David
>>>> N1RO/VE3TMK 
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>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
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