[JMS] 90801 (90800)

[Don Buska - The Radio Lab Works]

Hi Wilson,

I think your title was suppose to state the 90800, as the 90801 used the 
5763-6146 line-up.  Sorry can't provide much insight into the 90800, but 
there are many in service with the group members.  From our webpage the 
90800 was "based on a transmitter published in QST November 1940 by Don 
H. Mix, as "A Simple Two-Tube Exciter". It also made its appearance in 
several editions of the ARRL Handbook for the early 40's.  So yet again, 
this was essentially a QST project made into a product by the Millen 
company.

73
Don N9OO

On 11/25/21 7:58 PM, Wilson Lamb via James_Millen_Society wrote:
> Do we have any actual operators of the 807 exciter?
> I have one now and am planning to drive it with my Variarm.
> Does anyone know where to find a genuine Millen schematic?
> I have one from the web, but it's not stamped, so I don't know if it's accurate.
> It's been interesting to start looking at the exciter, which seems strangely designed, to me.
> Why a 6L6 first stage?  It's not a great osc tube and is WAY too big for driving an 807!
> Even going down to a 6V6 seems more reasonable.
> And how strange the rig throws away bands by not being able to run the 6L6 straight through.
> If one has a Variarm, 90700 version, one cannot operate 80m, because of the 6L6 problem.
> Looking at the schematic, it seems I can jump3 and 5 on the 6L6 socket, with the B+ disconnected from the tank coil, and plug a B&W coil into the xtal socket.
> I don't have the coupling unit for the Variarm, so I could feed it to the link on the B&W coil and be all set.
> My Variarm puts out a solid 2W on 80m, which should be more than enough to drive the 807.
> And is the 807 reliably stable?  They are notorious oscillators and the 90800 has no neutralization or even a parasitic suppressor in the plate!
> I want to run the 807 with fixed cutoff bias, as recommended in the manual, but with osc keying, so it has to be stable key up.
> And why in the world would anyone bury all those components in a skinny chassis, with very poor access?  Any serious work around the osc socket will require removal of components!  Using a removable top plate on the chassis would solve this problem.
>
> Speaking of design, my unit has a variable coupling cap, but it's shown as fixed on my schematic.
> The manual talks about changing it if more drive is needed, so I expect mine is a retrofit?
>
> I don't have a lot of time for this stuff, but will plug along until it's working reliably, so I can use it in CX.
>
> Any operational experience or voltage measurements would be appreciated.
>
> BTW, the Variarm is quite stable and has a fine note, very usable.
> I've talked to SC, IL, MA, NY, and PA, mostly with good reports and I have good reports, amazing really, from NH and VT on the Reverse Beacon Network, amazing!
>
> Wilson
> W4BOH
>   
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