Radionette K3

[Cornelius]

I'm doing an overhaul for a friend of mine, and wondered if anyone have a schematic for this Radionette K3?

It has 4 EF86 preamp tubes, one 12AX7, and four 6L6GC output tubes, rated at 50W output. 4, 8, 16 and 32 ohm speaker output plus an 100V speaker output. 2 microphone, 1 turntable and 1 tape input.

Some photos for you to enjoy... (full size photos at my gallery: http://www.mwlmf.net/gallery/RadionetteK3 )
[img:800:600]http://www.mwlmf.net/albums/RadionetteK ... .sized.jpg[/img]
[img:800:600]http://www.mwlmf.net/albums/RadionetteK ... .sized.jpg[/img]
[img:600:800]http://www.mwlmf.net/albums/RadionetteK ... .sized.jpg[/img]
[img:800:600]http://www.mwlmf.net/albums/RadionetteK ... .sized.jpg[/img]

I'm guilty of some of the earlier repairs (done in my youth; 25+yrs ago), for instance the big power resistor seen on the top-view photo; the old resistor was almost as big, but broken in three.

The amp are in working order, and have a very clean and warm sound, so i'm not going to do much here, just shape it up a bit...

My friend complained about having to put the amp on it's side to get sound, and after a quick look, i saw that the 6,3V to the output tubes had a loose wire from the PT; putting the amp on it's side made the wire connect to it's soldering point... (look at the two yellow from the center of the PT in the photo of the underside...)

The cathode cap on one of the preamp tubes have one disconnected leg (the only bright-red cap there), so that's another to-do... Though, the cap are 100uF, so i think i'll lower it to 25uF.

There is no hum and very little hiss, but i can see that one of the filter caps (the two large metalcaps) have a rather large bulge underneath, so i'm considering swapping them...

New output tubes have been ordered...

I'm not depended on a schematic, but it would be interesting to see one...

[Aurora]

Hi Cornelius........
There's not many of us "Norgies" here, and I doubt that unit sold very much outside Norway, but then again you might be lucky..

Norsk Radiohistorisk Forening nrhf.no may have it - checked there...?

[Cornelius]

Oh, more than one Viking are probably many... I know there are more than you and i here, so let me count; One, Two, MANY!

Yes, checked with Nrhf... They're too attached to radiowaves, which we do the utmost to avoid in our constructions...

Swapped the 100uF red cap with one at 22uF, and didn't notice any sound change... But didn't expected to either...

I took a closer look at the filter caps at the PT, and the one with a bulge underneath (connected 2x40uF in series(?!) ) had one 33uF in parallel?! When i measured it (in circuit) it was rather erratic; it varied between 90uF and 150uF. I should probably disconnect the one with a bulge...
That said, i also have to admit that there are more hum than assumed... (First test was late in the night with an humming reverb connected... )

[M Fowler]

I live right smack in the middle of Norske country Minnesota and North Dakota, USA I am also mostly Viking myself.

[Structo]

That is one big power resistor on the front.

So this is a Hi Fi power amp?

[Cliff Schecht]

That's nicely built inside, for the most part. Look out for those Hunts capacitors though, they can be quite dangerous in that they fail easily with age. They are known for crumbling apart or developing cracks that eventually lead to open (hopefully) or closed circuiting. In my 6L6 Deluxe build, I gutted a hifi build that was full of those same brown colored caps. I was thinking about reusing them until I googled "Hunts capacitors" and saw how bad they really are..

[Cornelius]

Well Mr Fowler, you keep that axe sharp then; no knowing what will happens... Yes i understand that many Norwegians settled there when they migrated in the late 19-century... Wonder how it would have been here if they hadn't...

That power resistor are about 1/3 larger than the original;; it was what i had lying around, and it was adjustable...

And yes, a HiFi, without the Hi i'd guess... The frequency response falls off quickly after around 10kHz.

I am a bit worried about those Hunts caps; some of them have wax-drops, like they have been very hot... No cracks though...

I think the amp needs a more throughout overhaul, 'cause i cranked the amp all the way up, and the distrotion was terrible, like a kind of digital 20Hz tremolo... And mic1 and mic2 sounds distictively different... It's not designed for any overdrive though, but my friend will only use it with a guitar, so i might as well make it more suitable for it.

Edit:
Here's an overhaul page (in Norwegian) of a similar model; the K1 (12W stereo):
http://www.mantor.info/Hobbyhjornet/Rad ... onette.htm

[Aurora]

This is more of an installation type amp, given it's 2 mic inputs and 100V output......probably late 50s.. any date codes there?

For those interested, Radionette was one of Norway's larger radio and later TV manufacturers from the early days until it faltered in the 80s.
They made very good stuff in the heydays - before japanese competition killed them. Radionette was more or less politically forced into a merger with Tandberg in teh 80s, which subsequently really killed them both.
The brand name is still in use - don't know who owns it, though.........

[Cornelius]

Haven't done much on this amp yet, but i've disconnected the two 2x20uF caps in the power supply, and installed new ones on the underside of the amp; that way, it looks original from the top. This removed the hum, so those old caps was no-good...

Now, there's 2 more 'multi'-caps in the power supply; those for the preamp tubes (two of the thinner cans seen on the overside of the amp). They are 2x 20uF, 450V + 1x25uF, 25V; the last part are the cathode cap for the output tubes.
The second Mic-input have some hum, so i think i'll replace these caps too.
Question:
Would it be ok to use a 25uF, 450V cap instead of 25V in the place where the Cathode cap are? (got loads of those... )

Another thing:
Please remind me; with a 8ohm speaker, pulling out 2 of the power tubes; should i connect the speaker to the 4ohm output or the 16ohm output?
(I know the answer are somewhere here but... )

[Structo]

Did you change the input to make it more guitar friendly?

You must have some good EF86 tubes as I have read that they can be very noisy.

[Aurora]

Of course you can use a 450V cap instead pf a 25V.......but why on earth would you???????
A 25uF/25v is 5 kr...? And prolly 10 times the size !
If you don't have one, I'd be happy to send you one when I get home..... around sept 10th or so........

[Cornelius]

Well, i do have some 25V caps but they're used, and those 450V i have are new - and i have lots of them... No other reason...

I haven't touched the inputs, since the owner like the sound as it is, and yes - there's some hissing noise when cranked up, but it's bearable. Putting your hand close to those ef86 tubes produces a lot of hum, but the whole amp case are of metal, so that's not a problem.

[Aurora]

Hi Cornelius... still here????

Did you find anything wrg to schematics for the K3???
- Just unpacked one - in deep need for some TLC....

[Cornelius]

Sorry, no.

After re-soldering the 6.3V wires to the trafo, and swapping those electrolytes, the owner was so happy with the sound that i wasn't allowed to change anything else, so i didn't pursue the search for the schematics... I guess NRHF is still the best bet...

I've been silent here for a while, but i haven't been idle; i've built myself 2 small amps; one Gibson GA-5 style (1x EL84), where i added a one-tube reverb, and one Stereo (common power trafo) Fender Princeton (6V6), for use with my Alesis QuadraVerb... The latter amp are still missing a front panel and a cabinet though... - And i now have a speaker shortage...