JohnnyGuitar
New member
Got curious after discovering this model on the Marshall website. It's only 30 watts but uses 2 5881s... So is it class A?
Marshall JTM 45 (2245) Class A or A/B
- Thread starter JohnnyGuitar
- Start date
guitfiddle
firstlessonologist
Re: Marshall JTM 45 (2245) Class A or A/B
It's AB
It's AB
James Rock
Active member
Re: Marshall JTM 45 (2245) Class A or A/B
It may be similar in how the power amp works to (more a then b but still ab just different biasing etc) and yes they technically distort at 30 watts but what we call clipping and scientifically are different things ac30's at least get more bloom and power before resembling distortion (and are loud at this point!)
Stratman
Guitaris Maximus
Re: Marshall JTM 45 (2245) Class A or A/B
Class AB is a push ~ pull design.
Manufacturers data for the KT-66 shows a single ended class A design running the KT-66 right on its anode dissipation limit of 24 watts. 13 watts of output is claimed at 10% THD. For a push-pull class A amplifier, the output figure would double due to the use of two valves, to 28 watts.
Further down the sheet, parameters for class B are listed. Claimed output is 50W at 5% THD - this is substantially higher than the 28 watts for the class A scenario!
Putting this into perspective, you would need five KT-66's to power a 50W amp in class A, and only one for class B. In the hybrid AB amplifiers, two KT-66's are generally used for a 45W head such as a Marshall JTM-45.
Note that GEC KT-66 tubes were used in the original JTM-45.
Class AB is a push ~ pull design.
Manufacturers data for the KT-66 shows a single ended class A design running the KT-66 right on its anode dissipation limit of 24 watts. 13 watts of output is claimed at 10% THD. For a push-pull class A amplifier, the output figure would double due to the use of two valves, to 28 watts.
Further down the sheet, parameters for class B are listed. Claimed output is 50W at 5% THD - this is substantially higher than the 28 watts for the class A scenario!
Putting this into perspective, you would need five KT-66's to power a 50W amp in class A, and only one for class B. In the hybrid AB amplifiers, two KT-66's are generally used for a 45W head such as a Marshall JTM-45.
Note that GEC KT-66 tubes were used in the original JTM-45.
Lake Placid Blues
New member
Re: Marshall JTM 45 (2245) Class A or A/B
Original 6L6 and 5881 loaded JTM45's ran around 27-30 watts at clipping according to Doyle. Original KT-66 loaded JTM45's put out about 35 watts at clipping according to Doyle, which is how all tube amps are, or are supposed, to be rated at. Maybe 45 watts flat out and distorting is where the 45 comes from?
My Metro JTM45 isn't quite as loud as my 50 watt Jubilees (which arn't as loud as most 50 watt Marshalls). It's plenty loud enough to gig with mind you, even with most drummers. It seems a bit louder than a Jubilee clicked down to 25 watts all else being equal.
I played a original 65 JTM45 once. It was loud but not like 100 watt plexi loud. I just remember it as having such a huge sound.
My 45 runs about 410 volts on the plates- biased hot. Most originals typically run around 425-430 depending on the exact transformers used.
Original 6L6 and 5881 loaded JTM45's ran around 27-30 watts at clipping according to Doyle. Original KT-66 loaded JTM45's put out about 35 watts at clipping according to Doyle, which is how all tube amps are, or are supposed, to be rated at. Maybe 45 watts flat out and distorting is where the 45 comes from?
My Metro JTM45 isn't quite as loud as my 50 watt Jubilees (which arn't as loud as most 50 watt Marshalls). It's plenty loud enough to gig with mind you, even with most drummers. It seems a bit louder than a Jubilee clicked down to 25 watts all else being equal.
I played a original 65 JTM45 once. It was loud but not like 100 watt plexi loud. I just remember it as having such a huge sound.
My 45 runs about 410 volts on the plates- biased hot. Most originals typically run around 425-430 depending on the exact transformers used.
