• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

"lift off " or "Houston we have a problem"

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music soothes the savage beast
Joined 2004
Paid Member
variac is the best, but if you dont have it, you can use incadescent bulbs

powering it trhough the bulb will tell you how much current it draws, if too much, bulb's too bright and eventualy burns depends on wattage

i suggest you test power suply separately first, lets say with three/four bulbs in series

good luck!
Lift off

As suggested I used the variac. I monitored the b+ and just had the rectifier in all was good 320 volts. I put all the tubes in and brought it up slowley......... 20 volts :bigeyes: . I checked each ch seperately
same same . I went in ... turned out had a bad connection from the B+ ground bus to chassis ground(star ground for the world). IT WORKS .......... . Thanks to every one who answered all my dum nub questions.


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Joined 2001
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Re: harsh

tenderland said:
I have a pair of 166, I would like to build the stock BHL enclosure on the Fostex Web site. What do you think about the harshness ?. This is all new to me , will the amp mellow out ?

A horn should help wit the speaker's balance... these are really designed for horns (you'd use the 167 for any other enclosure)... time should also help....i've also gotten good feedback on the addition of a phase plug.

I'll have to get a set of these myself someday and see how some of my mods work.... one thing that you should do is to ductseal the basket -- particularily the basket-magnet junction. Shape the ductseal here to smooth the exit shape of the back of the driver. A wool felt cap on the back of the magnet is also helpful (wrap it around the sides of the magnet and just use an elestic to hold it in place. Another trick is the 98 cent trick/tweak to damp the resonances at the edge of the whizzer & the cavity between the whizzer & the cone (do a search, there have been posts in just the last few days on this. These 3 mods are reversible.

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