The Swedish 30K-1 part 1 The Exciter

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 I got a trailer full of transmitter delivered in september. A transmitter built to order by one of the "Big guns" back in the 1950's, SM5RM. It was probably built by SM5LI around 1951, who at the time worked at Standard Radio in Bromma. Standard Radio was a swedish manufacturer of radio equipment, known for the military CT-450, RA200, SSA400, and amongst others the CR300 series of receivers.

The build quality is exceptional. Everything is heavy duty. High quality components from the SRT production line is used, and all of the chassis parts are beatifully crafted, panels are engraved etc.

Not that I needed another project, but hey, you can't pass 400lbs when it's being delivered to your doorstep.


Transmitter before it was taken apart for shipping




The transmitter sports 2x813 in push-pull in the power amplifier. Modulators are also 813's. There is a 2M transmitter in the rack as well as an antenna tuner, fully metered etc. The power supply contains a big oil filled HV transformer, a variac and a mil-spec modulation transformer, also oil filled. We can assume that the Collins 30K was an inspiration.

2x813 in push-pull


A fun thing is that when I asked about the transmitter on a forum, I got a screenshot of the sales ad from March 1963 QTC about the transmitter, put out by SM5RM.



It was sold in 1963, advertised as "professional, laboratory built, and in exceptional condition. For sale to a club or a very serious amateur".

The asking price was 6000 kr, roughly 85000kr in 2025 money worth, or about 9000$. 

SM5AZG bought it, and brought it north when he moved back to SM2 in the 1980's. AZG kept it all those years, but it was unfortunately stored in a cold barn, where moisture got to it, causing the metal chassis to rust. When he became SK, SM2CLY took care of the estate, loaded it up on the trailer and took it to me.


The start of the resurrection needs to start with the exciter, since it appears to play an important role in controlling the transmitter, also since it contains the speech amp.

The exciter was custom built around a Collins 70E-A8 VFO. They were sold as 310B exciters, but also as a barebones VFO containg the VFO and dial which was offered to homebrewers like SM5LI. My guess is that they bought a 70E-A8 and made the entire chassis at SRT. The exiter is bandswitched, 80-10M. The final is a 2E26, with a plate voltage of roughly 300V. Onboard the exciter is also an FM modulator. The tube lineup in the rf section is as follows: 6SJ7 oscillator, 6AG7 multiplier, 2 x 6AQ5 which also acts as multiplier stages, 2E26 final. The audio/FM section contains as follows. 6AU6 mic preamp, 12AU7 amplification stage, 6SN7, 6SN7 phase splitter, 2 x 6SA7 which provides FM modulation. (Or rather phase modulation). There are controls for clipping and mod level adjustment. The FM mod is meant to drive the 144MHz module that sits in the rack.

The Collins design goes in the exciter. Looks very much like a 32V series transmitter




Exciter innars. A capacitor says June 1951, which helps dating this to around 1951/1952







Note the Collins 70E-8 VFO that sits between the audio and RF sections. in the back sits the power supply, completely shielded.



Today I put the exciter on the bench to evaluate it, and to make a capacitor replacement list. Also, since the power transformer was missing, I needed to figure out what I needed to source for it.

Unfortunately, there were no schematics on the exciter, so I spent a couple of evenings tracing and drawing the schematic i KiCad. To determine how to connect the transformer I begun by measuring and nesting out the transformer wiring, and after the a few evenings I know what to look for. Everything is in really good shape considering it's age. A few wires have come loose, a few solder joints are bad, and of course, all of the capacitors needs replacing.

To be contiued.



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