Changing the speaker looks like an exercise in futility. If they all sound like crap that's not the issue. I would walk away and come back to it. There may be a mis wire. If tubes have been subbed with known good, then that cannot be the issue. The joy of having a few radio's lying about, is they are tube testers and if they are working happily their tubes are OK.

I have seen 6AV6 with shields and on rubber mounts. It compares favourably with 6U7 as being a nightmare tube. If there is a fault on the chassis they can exhibit microphonics. With no signal, like short out the antenna with a 0.01mfd (103) cap and raise the volume. If there is distinctive hum rather than a slight hum in the background, that would indicate a power supply issue like overloading. Overloading can cause hum: Hum can cause distortion. Hum modulation can start at the Pentagrid (6BE6)

You can pick up a 2nd hand Oscilloscope cheap OWON makes multimeters with them built in for not a huge amount of money. Fortunately I picked up a book from "John F Rider" exclusively on them and another I bought years a go, which is apparently sought after. I seem to have accumulated four. One given to me recently, condition unknown, a Heathkit OS-1with hum issues (board re-built once) a thirty dollar at a clearing sale BWD dual trace (needs a pot replacing) and Jaycar one.

Normally when an Oscilloscope breaks down you need a second one to fix it.

Thanks again, I have done just that and put it aside for now. Gets too frustrating after a while, will try & source some better equipment.
If I can grab some connections at Jaycar I’m keen to try hooking up my MP3 player to see whether that sounds alright - that would rule out the output stage.

Started tinkering on my old Kriesler 11-97 again….added a 100k resistor to phono input & got a nice little bass boost out of the sonotone which is good! Now to work out how to do that to radio.

Update: increased the c19s from .033 to .047s and have slightly more bass on radio in the Kriesler now….enough to keep me distracted from the hmv for now

You may have to make some sort of "Black Box" to connect. 11-97 to an MP3 Notables are that the signal is already amplified and will overload the pre-amps.

Info on the output circuits of the MP3, is vague. If its magnet there will be a problem: It is liable short out the tube bias and over load the preamp as its a direct feed into the grid if you use the phono plugs. So you may need something like 47K in series and DC blocking and that could damage the MP3 if you get it wrong.

That set is back biased and a misplaced ground can destroy the bias. That will affect all tubes. I note that it has a shielded power transformer so an earthed mains cable is desirable.

The overloading would be applicable to HMV and the difference is that you are trying to feed stereo into mono and you have to combine the signal before feeding into the HMV.

That's why I prefer using the radio wave method as its quick.

Thanks heaps for the help again! I was just going to try the mp3 on the hmv for now - by feeding to the volume control - I didn't think about overloading the tubes - I thought input to the volume control just goes to output tube but rechecking the schematic it looks like the volume control output goes through the 6av6 then to the output tube....if I use an adjustible volume mp3 would that perhaps avoid overloading do you think? I was just thinking of using my battery powered mp3 player with headphone output.

I hadn't even thought adding mp3 could affect tube bias.....could it affect it on just the Kriesler or both you think? Understanding the biasing is a bit beyond me.....kind of know the theory that tube needs bias so it doesn't 'run' when there's no sound and that comes from applying a small negative voltage to the grid.....and that the small negative voltage comes from a transformer tap.....but wouldn't understand the interraction between that and mp3 connection.......so tricky!

With the HMV you can likely feed across the volume control, or into the cathode of the 6M5. Where it will all come unstuck is with the output of the MP3.

Commonly solid state amplifiers do not use a speaker transformer: The Voice coil of the speaker is liable to be in the collector circuit of the headphones, or speaker/s. Therefore, should there be no auxiliary output (or even if there is) you might blow up the output of the MP3 if it is a coil and not crystal.

Like alignment the only way to block any DC is by the use of a series cap.

As an MP3 running on its own batteries there should be no argument between power supplies, unless MP3 is operated from a Wall Wart (Plug pack). Then there is a risk with some regulated power supplies going crazy.

Radio repairs do keep the mind active, there are traps.

Radio repairs sure to get the mind working! This forum is so helpful too I’d have made no progress with out it & your help.

I have been to Jaycar & picked up a switched 3.5mm socket to wire in which should be pretty simple.

I’m interested to see whether this distortion on the hmv is gone with the mp3 connected!

I figured I’d try a schematic I found online which is a resistor between channels to make output mono connected in series to volume control with a .01μF cap. Hopefully be some nice clear sound - unfortunately seems hard to get that with am reception nowadays.

May eventually try similar on the Kriesler but that seems to pickup am stations better & with the gram for vinyl it provides some great listening sessions. I still have right channel intermittently dripping out but seems to be cartridge bc when it cuts out & I lift arm & touch stylus I hear sound from the right channel. I might try adding a pre amp & upgrading to magnetic cart when it gets worse - I added 100k resistors on input so it has quite substantial bass now which sounds really good for the most part.

I got the switched 3.5mm plug in - wired up to volume control with 1k resistor between channels. Also a .1μF cap for ground to chassis.
It works - I had a .01 cap in series to volume control but it wouldn’t work.
The volume needs to be cranked up to full for decent sound though - could the .1μF to ground cap cause this?
Or is the 6m5 just too weak to add much?
But anyways it works!

On the American Forum running commentary on two different sets in the one post is banned as it can cause immense confusion.

One big problem is we have no idea if the headphones if it uses them are actually dynamic, or something else? You possibly need 1.5V of swing to drive the 6M5, we have no idea if the MP3 can do that, or it needs the 6AV6 as the pre amp?

the 11-97 being stereo has listed on the circuit two switched jacks one for each channel. There may be a commercial adapter other wise you may need audio transformers to adapt and that is done. Again for coupling purposes we have no idea of the MP3 output.

It may have to be a case of taking the risk of using an ohm meter to see if there is something like 33 Ohms resistance on each earpiece.

This is a haphazard way to sort out these sets and not the way I would go, as I have equipment to do it differently.

If the MP3 is running on batteries, and not in contact with the mains there is only a need for caps on the output.

That is the post! I used 2nd schematic with the switched socket but a resistor tying the r & l mp3 channels together instead of a cap.

Hmmm I’m just a little confused why radio wouldn’t work with a coupling cap on output?
The cap has to be on output of switched socket which meant radio signal also ran though it - but radio wouldn’t work with that in?
I didn’t actually test MP3 player with the coupling cap though - just radio….cap was just a .01 μF.
Maybe leaving this out is messing up dc voltages reducing input of mp3 I don’t know.

The avc wouldn’t be getting interfered with by adding the cap in radio signal line to volume control would it?

I have revisited this today and tried a .02μF cap on input to volume control but it still won't work on radio....but it does work using mp3.

The radio input comes from pin 4 of IFT2 to the switched 3.5mm socket.....then output from the switched socket runs to vol control through the .02μF cap.

There must be something else going on with the line from the IFT2 to the volume control that needs DC to pass...or that I'm reading the circuit wrong?

How important is a cap between the mp3 and vol control?

I suppose I can abandon the switched 3.5mm socket and place a switch in and add a non switched female 3.5mm socket cable that has a cap in it that will then only work when using mp3 input but let the dc pass from the IFT2 to vol control on radio....or I could just leave the cap out. I could also use a switch to disconnect radio audio somewhere else too I guess?

The other thing is that volume basically needs to be at full to work....I replaced the 1k resistor between mp3 R&L channels with a .01μF cap to see whether the resistor may have been reducing too much of the input on one channel...but it has not made any difference.

Your idea of using 6va6 as preamp may be necessary here....in which case do I simply take mp3 input to the 6va6 grid - using a coupling cap perhaps .01uf?

The MP3 is stereo I would assume? If so the stereo has to be recombined in such a fashion that it does not short out the output of the MP3. Americans are doing a lot of this sort of thing, so there may be a commercial coupler made.

You will be able with the MP3, if you use the volume control of the MP3.

The connection will be pin 1 of 6AV6 via a capacitor and the earth of the MP3 to ground.

Yes it is stereo - I’ve joined the channels with with a .01 cap.

I think I’ll remove what I’ve installed and input a switch to 6av6 with a cap as mentioned.

What would your recommended way of disconnecting radio be in that instance?

Hopefully almost have this sorted - thought this would be easier haha

Initially I would see if it works then worry about switching. which can be done with a 3.5mm or 1/4" stereo socket.

Using the normallising pins.

Well I tried direct to grid but doesn’t work - must not be enough voltage supplied from mp3 to connect to 6av6 grid.

Incidentally looking at schematic it seems like - but I could be wrong - That volume control is before 6av6?

Anyway I’ve made a female 3.5mm audio socket & cable with inbuilt 600 ohm resistors for each channel combining thereafter & .047 cap to run to a dpdt switch which basically either connects iftf2 or mp3 to the volume control.

Volume needs to be cranked up heaps to hear mp3 but it works and has a cap in series now at least.

Doesn’t sound anywhere near as nice as I expected though - not sure I’d bother with all the hastle again! Although at least there’s no distortion on mp3 - that is a bonus!