Small Special without a Choke?

[lord preset]

I'm putting together a 50W Small Special using an 70's Peavey Classic as a donor amp. All of the Small Special builds I've seen on TAG have used a choke, but I'm wondering if anyone has built one with a resistor instead? I've yet to build an amp with choke so it's hard for me to visualize what I may or may not be missing in not using one here. I ask because I have 10W resistors but don't have a choke and my "Order Now" finger is tired.

[jelle]

resistor works just fine.

[jelle]

Any luck?

[lord preset]

Any luck?

Funny you should ask. I've had excellent luck in that I built it, but less than good luck in that it doesn't work Details.

I built a power supply following the original peavey design and have all the expected unloaded voltages. It passed the tubes out light bulb test but not with tubes in. Ive narrowed it down a bit. The preamp/PI section does pass the light bulb test but when power tubes are included I get the initial expected flash then it dims down to a nice low glow, then after a few seconds the build grows increasingly bright before I turn it off. B+ drops steadily as the light brightens and no idle hum from the speaker.

I have not found any shorts. I am thinking I have a bad OT. It seems to pass simple resistance/continuity tests but the donor amp was known to not be working when I got it and I discovered that both speakers in the combo were dead as dodos. If the previous owner tried to run it like that - well , nothing good can come from that, except maybe that I got the amp for nothing.

[jelle]

Did you try different powertubes?

[lord preset]

Did you try different powertubes?

Yes - two different tested-as-good sets. Also I just replace the original tube sockets in case there were hidden carbon traces, etc.

[xtian]

What wattage bulb in your limiter? Cause if you've got a big one in there, like 100watt, it may let enough current thru to power the heaters hot enough to get the power tubes working, at which point they start pulling current, and your bulb gets brighter.

Just a thought.

[lord preset]

It's 60 watts. I've used the same limiter setup,to test previous builds and have never seen this behavior. As I metioned earlier, the speakers in the combo were complete toast as in burned open so it's not hard to imagine that the OT is damaged. I don't have one lying about to try but i need to get one anyway for a later build.

[jelle]

The power consumption of your 50W amp is much more than 50W.

[xtian]

If your OT was bad, in a way that sucked current to ground, it would do it immediately on application of B+, don't you think?

[lord preset]

If your OT was bad, in a way that sucked current to ground, it would do it immediately on application of B+, don't you think?

You may be right. It appears from reading that OTs have a variety of failure modes so I was thinking this might be one of them. But what do I know?

[jelle]

Have you considered starting it up without the light bulb limiter, and relying on the fuse?

[lord preset]

I have considered it but I am really very cowardly. Is there any chance that a bad OT or undiagnosed short can take out the PT before the fuse blows? There is a 3 amp fuse in there now, original to the amp.

[jelle]

It is possible, of course. But the info you have given so far does not alarm me yet. I expect that 60W bulb to go bright. And the fact that it is happy without tubes is good too.

[martin manning]

What is the bias voltage at this point?