Hi everyone, I have restored a Kriesler 11-30 table top radiogram. It works fine except the high notes are ear splittingly shrill and it lacks bass. I exchanged the speaker for several others to no avail.

The problem is also evident from the turntable so it's in the amp section somewhere. I refitted the speaker in the cabinet to see if it improves but the improvement was negligible. I have the two position tone switch in low, it's awful in the high position. I have replaced the 6M5 also to no avail. All wax and electro caps have been replaced but no micas.

Do you have any ideas? Thanks in advance

Link to 11-25 (no circuit for the 11-30) or 11-30 is in the AORSM

https://www.radiomuseum.org/r/Kriesler_11_25_2.html

Hi Tippy to clarify, is the sound via the radio tuner normal, but the phono is shrill?
Or is it shrill on both?
Fred.

Hi Fred, It's shrill from either source.

I'm probably exaggerating a bit, it tends to emphasize the highs more than the lows would be a better way of putting it. Voice doesn't sound too bad but music doesn't have a warm smooth sound and sounds a bit thin I guess. It's an 8" speaker but sounds more like a 4".

Possibly an audio coupling cap gone low in value?

Hi Irext, I had replaced the coupling cap and just checked it's value and it's 0.01μF as specified.

BTW... I like your Three Stooges avatar, I based my life on their teachings

I just received a NOS 6M5 and that seems to have improved it somewhat.

I tried the speaker in the cabinet and it was better but still sounded thin. I think I will reassemble it back into it's case with the turntable and the base fitted and check it again it may just be lacking the speaker 'box'.

it may just be lacking the speaker 'box'.

Speakers need some form of baffle to stop the out of phase sound waves generated by the rear of the cone cancelling those generated by the front of it, especially in the bass frequency range.

Yes, agreed GTC, I'm just making a new masonite base now and hope to reassemble the radiogram tomorrow.

You haven't mentioned checking voltages particular bias on the 6M5 & is the speaker transformer the original one ? What type of detector does yours use 6AD8 or 6G8G ? Also replace C73B 500pf, it may not be your problem but I always replace it, can cause a few problems.

Also make sure that you did actually put the correct value caps in and on the correct side of the tone switch? C26B is 0.005mfd 113B 0.03mfd. Also check that there is not a decimal error in others.

I've come across this a couple of times before. The first time was the second filter capacitor went open. Strangely, the hum did not seem so bad. The second time it turned out to be a replacement output transformer of unsuitable ratio. Although it used a 6M5, the required impedance for the circuit was 15k. The replacement transformer reflected an impedance of only about 4.5 k, causing weak and high pitched reproduction.

Stuart

My apologises everyone, I was called away for a few days. I have finished reassembling the radio and the sound is much improved, it won't win any HiFi awards but is as good as can be expected. I replaced the old ceramic cartridge with a new Chinese one and the record player now sounds as good as the radio... if that's any recommendation.

Thanks you everyone for your help

Hi Rudolf, I hope you are well. The detector is a 6AD8, does that make a difference? The Bias on the 6M5 is approx 5.2 Volts it should be 6 Volts. The B+ voltages are down across the radio by about 12 volts but can't imagine that will make a noticeable difference I'll check that cap too, thanks

Hi Marc, I checked all the caps and they are correct, so easy to make a mistake there. I replaced the C26B (0.005) with a 0.0047mfd and 113B (0.03) with a 0.033mfd.

Hi Stuart, I wouldn't have thought of filter caps but now that you say it it would make sense, I'll remember that one I suspected the speaker and output transformer first up. The speaker and output transformer model numbers are correct and I checked the output transformer. I also swapped it with an identical speaker/transformer unit but the sound was the same and may have even sounded inferior according to my lovely wife.

I'll complete the few recommendations you all have made and call this one done. I've had Al Martino singing to me while I write this and its sounds pretty good apart from the wow. Cheers

The normal acceptable variance on voltage is 20%. The bias will be low if the voltage is low as the back bias is dependant on the cathode current. Often the voltage is low, if something is dragging it down.

However, 11-30 wiring diagram has an omission. If we look at 11-29 it has the twin filter cap shown, only this time it has values: This is significant. Why? : Because the smaller is the input cap the lower will be the voltage developed.

So providing that the transformer tapping is appropriate, having the 8mfd cap then the resistor and 16mfd cap, one can expect less voltage. R191 is bizarre; It is shown and listed 1500 Ohms but is not listed as centre tapped. On the other circuits it basically translates to 16μF to centre tap - choke resistor (1500) - and 16μF to ground (chassis).

No wonder we have problems.

Yes, I agree, the voltages are within acceptable limits Marc.

I didn't think to look at another circuit diagram and I was unable to read the text on the old double cap to determine which was the 16 and which the 8mfd. I installed the 16 first in the line then the 8 at the resistor centre tap as that seemed the logical way. I think that's the way you are suggesting is correct and as is shown in the 11-29 diagram.

Yeh! 16 first 8ct of resistor and c53 elsewhere on the "B" rail.

Line voltages are always fun. According to the UPS here its running 234-237V with a steady load on it. The New transformer was set for 240 at its OP & is 60metres away. Previous was getting ready for a catastrophic fail. Age not known & it was second hand when installed so somewhere near 40 would be reasonable. Pictures taken of it, it was throwing out oil & the dirt was half way up the HV insulators, so it was getting to the point of flashover.

It was at 252V and gaining before it got changed, which is right on the upper limit. As a result all of the radio's etc. here were set at 240 - 260 tapping.

City's are much more variable in many places. One gets a sag when everyone religiously decides to cook meals electric at the same time. Followed by a surge when its cooked.