Hi, can anybody tell me what BIAS I´ve to adjust for a Dumble style HRM amp (100 watt) with four EL 34?
Thanks
Markus
BIAS for Dumble amp with EL 34
Moderators: pompeiisneaks, Colossal
Re: BIAS for Dumble amp with EL 34
Objectively it is best to get a reading on your plate voltage, decide which tubes you are going to use, and work from there. Some tubes, even within just the EL34 type, can handle a higher bias due to higher wattage specifications.
Subjectively, some people here like to run their amps colder and some like to push the envelope on the bias. Just be aware that you can wear out your tubes faster the harder you push them.
You should probably get an amp tech to measure your amp's plate voltages and give you an opinion of the range that is good for the tubes you are planning to use.
Completely dumbed down without knowing the plate voltages or the tubes you are using, 30-35mV average across all your tubes is a good target and you'll probably be in a decent range for both tube life and tone.
Subjectively, some people here like to run their amps colder and some like to push the envelope on the bias. Just be aware that you can wear out your tubes faster the harder you push them.
You should probably get an amp tech to measure your amp's plate voltages and give you an opinion of the range that is good for the tubes you are planning to use.
Completely dumbed down without knowing the plate voltages or the tubes you are using, 30-35mV average across all your tubes is a good target and you'll probably be in a decent range for both tube life and tone.
---------
Bryan
Bryan
Re: BIAS for Dumble amp with EL 34
If you don't feel safe and comfortabe reading high voltages inside the amp, there are several devices that can measure it from outside the amp.
Bias Rite http://taweber.powweb.com/biasrite/br_page.htm
compu-bias
expensive http://www.compu-bias.com/discription.shtml
Bias Probes http://www.ebay.com/sch/items/bias%20pr ... d=1&_sop=2
Amp Head http://www.amp-head.com/
Just to name a few
Bias Rite http://taweber.powweb.com/biasrite/br_page.htm
compu-bias
expensive http://www.compu-bias.com/discription.shtml
Bias Probes http://www.ebay.com/sch/items/bias%20pr ... d=1&_sop=2
Amp Head http://www.amp-head.com/
Just to name a few
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: BIAS for Dumble amp with EL 34
Markus wrote:Hi, can anybody tell me what BIAS I´ve to adjust for a Dumble style HRM amp (100 watt) with four EL 34?
Thanks
Markus
I'm assumming this is a conventional power supply and not the MM 700 volt style supply. The 183 layout has 30.3 listed as documented bias at 465V. I biased my 183 at around 39.5 with 462V on the plates, but that was with Gold Lion KT77's which I found an odd tube to bias.
If this is the MM supply, you need to be in 19-24 range.
TM
Re: BIAS for Dumble amp with EL 34
I would guess his amp is a Ceriatone, just a guess. 
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: BIAS for Dumble amp with EL 34
Maybe he has another DumbleStructo wrote:I would guess his amp is a Ceriatone, just a guess.
TM
Re: BIAS for Dumble amp with EL 34
Oh yeah, I forgot about him buying #94.
He might have picked up a real HRM.
He might have picked up a real HRM.
Tom
Don't let that smoke out!
Don't let that smoke out!
Re: BIAS for Dumble amp with EL 34
Structo wrote:Oh yeah, I forgot about him buying #94.
He might have picked up a real HRM.
That´s right
It´s a Bludo HRM with EL 34. Some more questions
?