Tube bias

[McMiRA]

I've been enjoying the sound of my Lafayette stereo 230a now ever since I picked the ol gal up. She has a slight humm when nothing is playing but its not noticeable to my ears otherwise. I think I need to play with the bias but have not found any information at all on the 230a on the Internet. It's like it doesn't exist. Does anyone know where I can find the recommended settings for it or maybe even a manual? This will be my first time doing this so I don't want to damage anything

[tube fanatic]

I vaguely remember Lafayette having a receiver, which I think was the LA-230, which used 6BM8s in the output stage. Is that what you have? I don't recall though if the tubes were run single ended (i.e. 1 per channel), or push-pull (2 per channel.) If the former, there's nothing to bias. The slight hum, if the electrolytic caps in the power supply are original, is likely originating there. More details, or better yet, a nice clear picture of the top and bottom of the chassis would be useful. A manual should be available from A.G. Tannenbaum: http://www.agtannenbaum.com/l_cat.htm#lafayette

Maynard

[McMiRA]

I don't know how its ran but I can tell you that there are two pots on the back right that say something along the lines of hum bias or hum balance. When i get home i will have to look at it and get pics. It is an integrated preamp, has 3 regular inputs, mm phono input, and one preout. This is my first venture into tubes. I picket it up extremely cheap with new tubes installed in it. When I auditioned it there was no noise at all, BUT I was also not on something as sensitive as a la Scala. She is rather ugly, I thought of doing some Frankenstein work on it and getting a new face ball milled and anodized and new cover and nobs to make it look like it belongs in my av rack. I will keep the origional stuff in a box if I ever sell it. For now, I'd just like to make it quiet and then ill go from there.

[tube fanatic]

Hum pots are normally used in the filament circuit, not for biasing. They can be simply adjusted by ear for minimum hum from the speakers. But, I'd still like to see pix of the top and underside of the chassis if you get the chance to post them....

[McMiRA]

I will ill out the amp tonight and take the lid off. I looked through the link and did not see a manual for it. The model number might differ from the lettering on the front, I will take a look when the lids off. Thanks

[JBryan]

Not familiar with your receiver but back in the days before polarity plugs (and ground pins), if you heard a hum you could simply flip the plug and sometimes, it actually worked. Also, most tube amps had hum pots - some easier to access than others. Finally, dust and corrosion could be the culprit so a thorough cleaning with DeOxit may be in order...couldn't hurt.

[Taz]

I've been enjoying the sound of my Lafayette stereo 230a now ever since I picked the ol gal up. She has a slight humm when nothing is playing but its not noticeable to my ears otherwise. I think I need to play with the bias but have not found any information at all on the 230a on the Internet. It's like it doesn't exist. Does anyone know where I can find the recommended settings for it or maybe even a manual? This will be my first time doing this so I don't want to damage anything

In the 1960s, many Lafayette brand radios were rebranded Trio-Kenwood sets...................

I happen to have an operating manual for the Trio-Kenwood KW-70U tube receiver, also sold as a Lafayette LR-800.............

Don't know if this will be helpful, but I'll try in case it might.......... Hopefully someone with more smarts about this will educate us both!

On the back of my unit between the fuse and the left speaker conections is a HUM BALANCE adjustment, looks like a small flat screw with a locking nut. On my unit it is stamped "HUM BALANCE" and appears as in my manual....

*****Manual states .. REDUCING HUM........... The hum balance control at the rear of the receiver will enable you to minimizee any hum that may originate from the unit during normal operation. The procedure outlined below should be carried out with a turntable or record changer connected to the KW-70U....

a. With the pick-up arm at rest, set SELECTOR to PHONO, VOLUME control to maximum, BASS and TREBLE to their midway or "Medium response" positio, and all other switches set for normal stereo operation..............

b. Using a screwdriver, adjust the HUM BALANCE control for minimum hum from both speakers....................................................

AC LINE CORDS................

As a general means of reducing hum, the following procedure should be carried out:

1. Turn on all equipment connected to the receiver............

2. Reverse the AC wall plug from the receiver to determine which position provides the least hum. Leave in this position............

3. Repeat this procedure with the AC plugs of the other components, using the selector switch to select the component being tested..........

Making a single ground connection between the receiver and a ground point (such as the AC socket wall plate) may further reduce hum. The ground wire should be taken to a point as close to the input jacks as possible..................................................................

............................................Taz