Sound on the st208's

[Hydrolastic]

Hello guys. As you know I have been struggling with the sound out of the st208's We have a favorite for looks in the house the 1st208 concert hall (avatar) and its in the best shape. The 2st208 was the garage unit that stopped working suddenly. Its a American country style and its kind nicked up. They were both recapped and aligned. While the new miniature Rottweiler was teething I decided to put the concert hall in the basement. but a few weeks ago brought it back up since I think it is safe if we don't run out of chews for the pup. So I determined that the speakers (no horns ) were not working correctly and bought some spares off eBay. The tweeter cones were brittle and the oval 4x7 was missing most of its paper cone on one. The replacement 4x7 oval looked identical but its number was different I figured it was ok to use as the impedance was close 3.2 vs 3.6. I got them all in and was not impressed. Still sounded similar, better but the bass was really Flubbery sounding and mid was better but one oval is louder than the other. The Amp 175 is not biamped So I got the Klipsch's out.
They are the corner version of the Heresey 1 of 1980 vintage (8 ohm). Hooked them up to the leads that went to the woofers on each side of the console. Very similar sound, The bass has to be on minimum to keep from distorting and treble has to be up to 3/4 to sound ok but sounds like its in a tin can. It is the amp itself I think. The bass is Flubbery equally on both sides. I wonder if there is a test I can do to determine the speaker voltage is correct. Also because of the sound quality I can't tell if its stereo or not. How do you determine that with a voltmeter? Pup's name is Ruby.

[electra225]

'Mornin', Hydro! I moved your topic to the Magnavox board so it would get more exposure.

Before you try replacement speakers, might I suggest you check your audio tubes as a first step. Garbled, distored, flubbery bass may be caused by grid emission in a tube or by incorrect bias. Does it sound bad right when you turn it on, or does it sound okay at first then gets worse as it warms up? Check the grid voltage on the audio tubes, 6EU7, 12AX7 then also on the output tubes which are probably 6V6's. The AMP 175 was the father of the vaunted 93 series amps. Check the tubes for heater to cathode shorts and emissions on each half. Check output tubes for shorts and emissions. Make sure the cathode bypass components are up to snuff. Then clean the volume, tone and balance controls, making sure they don't have dead or dirty spots in them. It's not likely that even if the speakers had holes in one or more of them that would make the entire audio output sound bad. Adding new speakers to he mix before you have cleared the electronics of suspicion may be adding more trouble that you don't need. Then go over each component in the chassis to be sure you have not used a replacement cap that is out of spec by a factor of 10. It happens. Check audio tubes in the tuner as well as in the amp. It might also help to tune to a mono FM station to check to see if the stereo is working. You can also connect a VTVM set to a low AC scale across the speakers to check balance when using a mono signal. Play a mono record if you have one. Obviously, you will need two meters, one on each channel. I would use an analog meter with a needle you can follow. Digital jumps around too much for this purpose. Just for grins, bridge the filter caps with new ones. See if that makes any difference.

Another suggestion would be to use a signal tracer to pick off the signal, starting in the pre-amp sections then moving to the amp to see where the signal gets "dirty". This might give some indication where to start looking. Good luck.

Cute puppy, by the way. He will make a dandy dog. Congrats and good luck. We are here to help any way we can.

[Motorola minion]

One item a friend recently found in his 9300 amp was an open cathode resistor. 100 ohm 5 watt. Check the voltages on your 6V6s

This will affect the bias and since both channels are distorting, as prime suspect as the power supply itself. I have this same console, restored (recapped and resistors over 10% replaced). But with original tubes like mine, yours should sound fine also, using 12 or 15 inch woofers.

[electra225]

The cathode bias resistor was burnt in two in my Imperial, burnt internally. That gave it not only garbled audio, but also a nasty hum. The output tubes were running wide open. That is really hard on output transformers.

[Motorola minion]

Forgot what mine was changed to, use at least a 7 watt resistor in this pole position, not a "dogbone" resistor your pup may be thinking of