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Peavey Series 400 Bass head speaker input getting hot!

D

D-Warrant

Guest
Jun 10, 2018
2
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#1
I just picked up an old Peavey Series 400 bass head and played through it for about an hour last night for the first time live. I have it going to a 2x15 cab.
The head is speced at 210 Watts at 2ohms. My cab is 600 Watts 2 ohms.
After playing I went to unplug the head from the cab and the input jack on the head was pretty hot as well as the male end of the speaker cable. The jack on the cab was fine, no heat there at all.
What could be causing this? I have never had any amp do this before and want to be sure it's not going to hurt anything before I keep playing out of it.
 
#2
The whole back panel on this amp is the heatsink for the output transistors. Because the speaker jacks are mounted to the back panel, they will eventually heat up to the same temperature as the heatsink. Additionally, because you are loading it down to 2 ohms, this increases the current through the output transistors causing more heat generation than a 4 or 8 ohm load would. The additional current through the 1/4" jack and plug might contribute a little bit of additional heat too. Are you using an actual speaker cable with 18 AWG or bigger?

All in all, it's probably normal for the plug to eventually warm up if the amp is working hard.
 
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#4
And an inherent symptom of the crappiness of 1/4" connectors handling power. Cheap/bad connector, small contact area == heat and lost power . . . If all you have is 1/4", at least make sure to use the heavy duty (Switchcraft 188 or similar) ones, especially at 2 ohms (200 watts at 2 ohms is 10 amps through the connector - well beyond the rating of a lot of 1/4" plugs . . .). If you have Speakon as an option, use it! This is one of the multiple problems that Speakon was designed to eliminate!
 
#5
tadawson said:
And an inherent symptom of the crappiness of 1/4" connectors handling power. Cheap/bad connector, small contact area == heat and lost power . . . If all you have is 1/4", at least make sure to use the heavy duty (Switchcraft 188 or similar) ones, especially at 2 ohms (200 watts at 2 ohms is 10 amps through the connector - well beyond the rating of most 1/4" plugs . . .). If you have Speakon as an option, use it! This is one of the multiple problems that Speakon was designed to eliminate!
Click to expand...
Wait a minute, this has nothing at all to do with 1/4" connectors on this amp. The jacks mounts directly to the aliminum back panel which is the heatsink. The jack will be about the same temperature as the back panel, around 150 - 160 degrees F.
 
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#8
byacey said:
The whole back panel on this amp is the heatsink for the output transistors. Because the speaker jacks are mounted to the back panel, they will eventually heat up to the same temperature as the heatsink. Additionally, because you are loading it down to 2 ohms, this increases the current through the output transistors causing more heat generation than a 4 or 8 ohm load would. The additional current through the 1/4" jack and plug might contribute a little bit of additional heat too. Are you using an actual speaker cable with 18 AWG or bigger?

All in all, it's probably normal for the plug to eventually warm up if the amp is working hard.
Click to expand...

I am using a speaker cable. I don't know what it is rated but it's much thicker than a typical cable. I would imagine it would be more than enough to handle the load.
It's good to hear that it's pretty normal for this to hear up. I just didn't want to harm anything.
 
#10
tadawson said:
Are you absolutely certain? I've had failing 1/4" get almost too hot to touch due to resistive loading . . . at 2 ohms, either (or both) could be in play, and we don't know what the plug/cable is . . .
Click to expand...
In the case of this amp (and other Peavey products of this era. Yes.
 
#19
Well, fortunately there isn't much in the power supply that could cause oscillation.

I'm assuming you have a decent analog scope (digital scopes are generally not a great choice for this sort of work).
 

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