Trio KW33

[Dandy]

You may not have made a mistake. But you could check your work with the help of your good photos.

Did the seller say it was working before? Are all the tubes in the FM section correct and working? You can check from your block diagram and schematic.

Hey, you've got half of it working (and the most important part) and now just just reached the next phase of the servicing. I don't know how to do RF fault tracing but others here do.

 

[gadget73]

Unlikely anything you changed in the tuner would have totally knocked out both bands. At worst, I'd expect misalignment on one band, or maybe weak performance. More likely something is in backwards or a lead broke from another component. Looks like the only parts changed are in the area right behind the tuner flywheel. I'm taking a flying guess at this based on physical layout, but I suspect thats probably the detector area. A broken lead in that area could kill both bands if there are shared parts. I do see 4 diodes, so either its the multiplexer output, or its an FM detector design I'm not real familiar with. Typically ratio detectors use a pair of diodes, not 4. MPX outputs will sometimes have 2 per channel.

Not sure what the two tubes front center are for, but it looks like there are new caps from the IF transformers there. Check the solder joints on those too.

 

[RWood]

Or....dare I say...... an antenna?
I've done it....er, not done it m'self.

 

[jwhvt]

Awesome! Based on your comments, I simple wiggled all of the tubes rigourously in their sockets and voila! FM! AM doesn't seem to be working but I don't really care about AM and maybe there's something else I'm missing.

Thank you, thank you! Feeling much better now.

The various FM options are confusing... FM, FM-Monitor, and FM-Receive. FM seems to be mono, FM-Receive is stereo but I'm not sure what the purpose of the FM-Monitor position is.

 

[gadget73]

does it play from one channel in fm monitor mode? maybe AM/FM simulcast stereo if it does. Usually you'd have 2 tuning knobs if it uses that system.

 

[jwhvt]

does it play from one channel in fm monitor mode? maybe AM/FM simulcast stereo if it does. Usually you'd have 2 tuning knobs if it uses that system.

No it plays both channels but it has a different sound then the plain FM setting... sort of dull and flat.

I did find this in the owner's manual. It sounds like in Monitor mode, it only picks up broadcasts that are in stereo. Since just about all the stations on the FM band broadcast in stereo, it pretty much duplicates the mono FM mode. So today, the Monitor --> Receive sequence seems like an unnecessary extra step.

 

[gadget73]

I love obsolete features on equipment. Its interesting to see the thought process. I have a Trio multiplex adapter that lets me tune in the sub-carriers. Nothing uses those anymore, but I have the option now.

 

[Dandy]

Yeah, I know the feeling of not understanding why there are some features, but great to have the FM signal playing loud and clear. My Trio's FM reception pretty amazing with a basic antenna.

Looks like you're there.

 

[jwhvt]

I have it hooked up and playing. I'm not crazy about the FM sound (a bit harsh) but I do like the sound through the AUX and Phono inputs. It also has a bit more hum than I like. My Grundig console pull was dead quite. I've been reading up on possible ways to reduce hum.

 

[Dandy]

To chase down the hum, you might try inserting the signal directly to the grids of the first of each pair of 6BM8s. Pin 1 of V15a and v17a (on my schematic). Detach the connection there first.

Obviously use a pot or preamp to control the level from a CD player. It should sound pretty quiet there. This should show that the hum is coming from upstream.

 

[jwhvt]

To chase down the hum, you might try inserting the signal directly to the grids of the first of each pair of 6BM8s. Pin 1 of V15a and v17a (on my schematic). Detach the connection there first.

Obviously use a pot or preamp to control the level from a CD player. It should sound pretty quiet there. This should show that the hum is coming from upstream.

Hmm that sounds pretty adventuresome given my skill level. I see sparks and smoke in my future...

The hum is there on both channels with the volume all the way down, and with any input selection. It doesn't really increase much with the volume control. I did try reversing the plug but I don't think it did much. The hum isn't terribly objectionable but it is noticeable compared to the Grundig. All in all, it's very pleasant sounding. I'm just going to play it for awhile before deciding whether I need to get back into it.

 

[jwhvt]

To chase down the hum, you might try inserting the signal directly to the grids of the first of each pair of 6BM8s. Pin 1 of V15a and v17a (on my schematic). Detach the connection there first.

Obviously use a pot or preamp to control the level from a CD player. It should sound pretty quiet there. This should show that the hum is coming from upstream.

If people are still willing to provide advice, I have a few additional questions.

First, Dandy, are the connection points you're suggesting I insert a signal on be on V12 and V14 on the schematic below? Also, I measured voltages at several points and compared them to the schematic. Do they look alright? Some look a bit high to me. If so, what do I do to get them where they should be?



Second, regarding the hum, could my PS filter cap arrangement be a problem? I thought I was pretty clever getting the replacement caps to fit underneath but could the placement be causing hum? Some of the white wires running underneath the cap connections carry 60Hz line voltage.




Finally, can someone tell me what the numbers in the diamonds refer to? I assume they're a measurement of some sort.

 

[kvflyer]

Those diamonds may be a reference number to a location in the circuit that is referred to in the factory service manual. Could be a chart that shows voltages in a table for ease in locating the specific circuit.

 

[Dandy]

Yes.

Disconnect the input signal to the grid of V12a (left channel) & V14a (right channel) (GREEN). Make sure the feedback network is still connected.(ORANGE)--I think, I have that right.
Apply the input signal between the the 50K and ground of the pot. Take the signal from the wiper to the grid of V12a.

I've tried to show this on your schematic.

 

[RWood]

From your description of the hum it does sound like it is from the power supply.
Since you have ss rectification - voltage doubler at that - I would increase the value of the 100uF caps to at least 220uF and I'd probably increase the 40uF that feeds the power tube screens to 80uF or 100uF.

As for rerouting those AC wires, I wouldn't think they'd have a major impact as long as they are not near signal-carrying wires.

You might also think about your filaments. Do the tubes getting 6.3vac use twisted pairs? Are they clear of the signal / grid / input wires? It looks like it has a hum pot - does that make any difference in the nature of the hum?

 

[gadget73]

The AC wiring is awful close to the filter caps. If you aren't using that socket on the back, I might consider removing the wiring to it to help remove the chance of an AC hum being picked up from the wiring. If you can move the cap thats right next to the fuse holder, that wouldn't be a terrible idea either.

 

[jwhvt]

Those diamonds may be a reference number to a location in the circuit that is referred to in the factory service manual. Could be a chart that shows voltages in a table for ease in locating the specific circuit.

I think you're right. I see the same numbers referred to in the tuner alignment section. They indicate where to connect equipment to.

Thanks!

 

[jwhvt]

Yes.

Disconnect the input signal to the grid of V12a (left channel) & V14a (right channel) (GREEN). Make sure the feedback network is still connected.(ORANGE)--I think, I have that right.
Apply the input signal between the the 50K and ground of the pot. Take the signal from the wiper to the grid of V12a.

I've tried to show this on your schematic.

Thanks for the helpful drawing. Not sure yet when I'll attempt this.

 

[jwhvt]

From your description of the hum it does sound like it is from the power supply.
Since you have ss rectification - voltage doubler at that - I would increase the value of the 100uF caps to at least 220uF and I'd probably increase the 40uF that feeds the power tube screens to 80uF or 100uF.

As for rerouting those AC wires, I wouldn't think they'd have a major impact as long as they are not near signal-carrying wires.

You might also think about your filaments. Do the tubes getting 6.3vac use twisted pairs? Are they clear of the signal / grid / input wires? It looks like it has a hum pot - does that make any difference in the nature of the hum?

ok, upping the caps is a relatively cheap and easy thing to try although I'll have to place an order. As for the 40uF cap, are you referring to the C303 cap that is connected between R301 and R302?


It doesn't look like they did any wire twisting. All of the wiring is laid out pretty much in straight lines. :sigh:




As for the hum pot, it seems to have almost no affect. The hum I'm hearing is with the volume turned down in any selector position. I did try flipping the power plug... no affect.

 

[jwhvt]

The AC wiring is awful close to the filter caps. If you aren't using that socket on the back, I might consider removing the wiring to it to help remove the chance of an AC hum being picked up from the wiring. If you can move the cap thats right next to the fuse holder, that wouldn't be a terrible idea either.

If I decide to install larger caps, I may have to try my hand at stuffing the original caps. If I do that, maybe I can avoid the socket and fuse holder altogether (wiring would be as it was originally laid out).