1992 peavy mark vi bass amp repair

[Snake5150]

Got gifted a semi functioning mark6 bass amp. Have a few questions as I’m not a bass guy before jumping into repairs.

The amp has “parrelled” speaker jacks.

I need to know if hooking up a 4 ohm speaker will be ok for testing without damaging the transformer.
The amps manual page regarding speakers attached for ref.
Also it has some damaged “spider” type pots, these are pcb mounted. Question being is the 4th leg that’s by itself just for mounting or is it actually in the circuit?

[DeepBias]

Hi Snake5150, did you repaired the amp ...

4 ohm is the minimum total impedance for that amp, seems correct. You can connect two 8 ohm speakers, or one 4 ohm speaker, or many other combinations of speakers but never under 4 ohm total, higher is correct but it will result in lower volume output. The two speaker outputs on the back are paralled, so connecting two 8 ohm speakers, one into each of the output yields a total of 4 ohm.

I think the 4th leg on the spider pot is center tap to the resistive trace inside the pot, just make sure it is part of the circuit, or not. Look at the image linked below :

https://i.sstatic.net/2e9YF.png

[glass54]

NO!
The minimum load is 2 Ohms
ie 2 off 4R in parallel or 1x4R and 1x8R in parallel or 2 off 8R in parallel speakers are all OK as well as 1 off 4R speaker
See attached pix from original "Post 1" as per manufacturers spec.
Regards
Mirek

[DeepBias]

In the operating guide page 5 :
Speaker output jacks :
Provided for connection of external speaker(s). Minimum total impedance is 4 ohms.

Now looking at power amp specifications at page 6 :
250 W RMS into 4 ohms
400 W RMS into 2 ohms with DDT compression

Does it means :
At 4 ohms 250 W RMS (safe, recommended).
At 2 ohms 400 W RMS (possible, but the amp will run hotter and rely heavily on DDT and cooling).

[glass54]

Can't see any major difference between the two configurations (2R vs 4R load) as far as output tubes are concerned
Same Voltage/currents in output tubes and Transformers.
You could argue that the DC resistance of Output Tx windings will contribute to slight differences in losses 2R vs 4R, but then there is the resistance of speaker cable (and associated losses), so you would be going down a rabbit burrow of speaker cable diameters, etc.
Its a tube amp, safer if you short circuit rather than have high impedance ie open circuit.
(The opposite is true for Solid state outputs)
What speaker (Impedance) do you have on hand?
Regards
Mirek

[DeepBias]

Can't see any major difference between the two configurations (2R vs 4R load) as far as output tubes are concerned
Same Voltage/currents in output tubes and Transformers.
You could argue that the DC resistance of Output Tx windings will contribute to slight differences in losses 2R vs 4R, but then there is the resistance of speaker cable (and associated losses), so you would be going down a rabbit burrow of speaker cable diameters, etc.
Its a tube amp, safer if you short circuit rather than have high impedance ie open circuit.
(The opposite is true for Solid state outputs)
What speaker (Impedance) do you have on hand?
Regards
Mirek

The Peavey Mark VI is a solid state amplifier.

The OP was asking for a safe impedance for "testing" without damaging the transformer, or even worst the output transistors (or MOSFETs) in the power stage.

Once the amp is repaired then he can give a try at 2 ohms but for testing and repair purpose, maybe it's better to go on the safe side.

Seems to have lots of fun tonight 

[glass54]

Thank you for refreshing my memory (BH400 output module SOLID STATE)
Not sure now what you are asking in regards to Post 1.
As per manufacturers specs, MIN LOAD 2 OHMS!!
You can run anything on that amp, 2R, 4R,.......Headphones etc 
BUT it will generate more heat at 2R load. Whatever impedance your test speaker is will be OK to use as long as it 2R or greater.
Your amp will require good ventilation if pushed and in that case make sure it is a Bass type speaker.
The only transformer stress will be mains transformer at very high levels, but will you be in the same room?
Enjoy your new amp 
Mirek