Soldano SLO 30 : How to bias check amplifier when replacing the power tubes (2023)

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For guitar amplifier technicians and electronics repair personnel...this video is educational only.
Do not attempt to measure voltages or repair an amplifier if you are not qualified to do so. Internal voltages can be lethal.
NEW TUBES : Sovtek 5881WXT, matched pair
Plate voltage ~ 430VDC (approx)...measure @ pin 3 of each power tube
Target Bias range ~ 34mA cool 60% ~ 37mA median 65% ~ 40mA hot 70%
Measure bias across R63 & R64 1-ohm resistors) with meter set to 200mV DC voltage range, 1mV~1mA
Adjust VR12 bias trimpot to set desired dissipation.
Recommend watching on 1.25X - 1.5X speed...I am from Texas so I talk slow as hell, sorry!
Paul ‪@gremlinmachineshop‬

Опубликовано:

31 дек 2022

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Комментарии : 23

@gremlinmachineshop Год назад

Also keep in mind with an SLO you are getting virtually all your gain & crunch from the preamp, so there's not much need to set the power section to a hot bias imho...better to run the tubes cooler and extend tube life.

@gremlinmachineshop Год назад

I think the TAD 6L6WGC-STR (small bottle design) will fit into the headshell dimensionally if you are looking for an alternative to the Sovtek 5881WXT.

@Matan2222222 Год назад

Thanks for the great video!

@gremlinmachineshop Год назад

FYI you can technically do the math for the 5881WXT as a 30-watt equivalent, but I chose to do a conservative rating BECAUSE one of the original tubes was wasted, possibly due to the factory bias being set at 70% for a 30-watt rating. Coulda just been a faulty tube though.

@bernardfoshage9901 Год назад

5881 tubes are so good though!

@robvoyles

I would like to bias mine very cold....counter clockwise would run them colder correct? my mesa boogies bias are not adjustable fixed bias ) and are biased very cold making it so easy to change tubes without a problem, i have been changing tubes in my mark III for 30 years without any issues as long as the tubes were good and obviously not shorted. do you know what turning the bias trim pot all the way left would be at its coldest bias and work? Thanks

@guitarscientist9386

what do you mean by the "all the tube drama that went down"? I havent been paying attention to tube news for a few years

@jthair1 Год назад

I just bought one of these and the gain on this amp is extremely compressed and over the top even on the crunch channel and I've played a few other ones. They were definitely more tamed than mine. Do you have a clue what it could be? Thank you.

@1974zah

Do you recall what the amp was biased at stock? Word is that SLO 100 are biased cold from factory, like 28mA. I understand the reasons why. Just wondering if the 30 were the same, and what might be your observations between stock and after you swapped tubes and rebiased.