18Watt.com

TriodeLuvr wrote: ↑

Sun 05/09/21 12:38 pm

The thing is, if the 125A is down 1 dB at 150 Hz, it's probably about half power (-3 dB) at the bottom of a 6 string. It would be interesting to know whether the Marshall OEM transformer is available at a reasonable price, or at least how it performs in this regard for comparison.

Jack

Let's start with the fact I use the 125A... wgat is the better alternative in output tube? Can I do better?

Off topic again: this is the result of the neck.. strung up:

Bieworm wrote: ↑

Sun 05/09/21 1:42 pm

TriodeLuvr wrote: ↑

Sun 05/09/21 12:38 pm

The thing is, if the 125A is down 1 dB at 150 Hz, it's probably about half power (-3 dB) at the bottom of a 6 string. It would be interesting to know whether the Marshall OEM transformer is available at a reasonable price, or at least how it performs in this regard for comparison.

Jack

Let's start with the fact I use the 125A... wgat is the better alternative in output tube? Can I do better?

Low frequency response is limited by the transformer's primary inductance, as well as core size, number of turns and voltage across the winding(s). The last three each create a finite limitation regarding core flux (saturation) at low frequencies, but which of them is the most significant is something only Hammond knows. In other words, it might be possible to achieve better low end response with a certain input impedance (dependent on tube type) and output tap, or some combination of ratios vs. output power, but knowing the best combination would require access to Hammond's internal engineering data.

Hammond does provide graphs showing response of the single-ended 125ESE at various impedance ratios. Generally, the low end is extended at lower primary impedances. Output impedance (4-8-16) appears to affect only high end rolloff. If the 125A behaves similarly, and if its published response specifications are worst case (presumably the highest primary impedance), then a different tube type or other technique for using a lower Z tap might be of benefit. The problem is, triodes with lower Rp generally have larger anode structures, therefore also higher dissipation and output power. So, we're no longer dealing with a 1W amplifier. It might be possible to manage this using a resistive divider or other than optimum biasing, but that would need to be worked out as a separate issue.

All things considered, locating a transformer with better performance is a much more satisfactory (and less experimental) solution. This is a niche market though, and small transformers don't entail the profit levels of their larger cousins. Nothing seems to be available as far as I can determine, the sole exception being the Hammond single-ended design. In the end, the main question in my mind is whether the sound of the Marshall can truly be duplicated without the OEM transformer. I do know the Hammond 125 push-pull series has been used in many low power amplifiers. Unfortunately, I haven't heard any of them live, and I have no direct experience with them that might be helpful in your project.

Jack

TriodeLuvr wrote: ↑

Sun 05/09/21 12:38 pm

The thing is, if the 125A is down 1 dB at 150 Hz, it's probably about half power (-3 dB) at the bottom of a 6 string. It would be interesting to know whether the Marshall OEM transformer is available at a reasonable price, or at least how it performs in this regard for comparison.

Jack

The reduced low end response will probably give better cut-through

zaphod_phil wrote: ↑

Sun 05/09/21 4:32 pm

TriodeLuvr wrote: ↑

Sun 05/09/21 12:38 pm

The thing is, if the 125A is down 1 dB at 150 Hz, it's probably about half power (-3 dB) at the bottom of a 6 string. It would be interesting to know whether the Marshall OEM transformer is available at a reasonable price, or at least how it performs in this regard for comparison.

Jack

The reduced low end response will probably give better cut-through

Maybe not. This isn't like turning down the bass control. The electronics driving the transformer won't benefit by not having to reproduce bass notes. The loss is occurring after the active electronics, so there's no corresponding increase in mid/treble headroom. Anyway, a bigger issue here as I understand it is that this project is for someone else. They want it to sound like the Marshall.

Jack

zaphod_phil wrote: ↑

Sun 05/09/21 4:32 pm

TriodeLuvr wrote: ↑

Sun 05/09/21 12:38 pm

The thing is, if the 125A is down 1 dB at 150 Hz, it's probably about half power (-3 dB) at the bottom of a 6 string. It would be interesting to know whether the Marshall OEM transformer is available at a reasonable price, or at least how it performs in this regard for comparison.

Jack

The reduced low end response will probably give better cut-through

LOL!!! what are we trying to cut through here? The wife doing the dishes or noisy children?

The Ampmaker OT worked fine for me playing through a 10" Greenback the guy I built it for bought.

Dd

Bieworm wrote: ↑

Mon 05/10/21 1:43 am

zaphod_phil wrote: ↑

Sun 05/09/21 4:32 pm

The reduced low end response will probably give better cut-through

LOL!!! what are we trying to cut through here? The wife doing the dishes or noisy children?

Are your kids baritones, and your wife a bass? Then it might help.

Bieworm check out the output transformer Dd mentioned at www.ampmaker.com, 4W push/pull,bandwidth 85Hz-6K Hz,output impedance 22.5K ohms.

geoff 1965 wrote: ↑

Mon 05/10/21 6:48 am

Bieworm check out the output transformer Dd mentioned at www.ampmaker.com, 4W push/pull,bandwidth 85Hz-6K Hz,output impedance 22.5K ohms.

I've read people have used the hammond 125A with success. That ampmaker OT has to be ordered in the UK. I'm from Belgium, ok we're neighbors, but shipping UK-EU is not that great at the moment with all that Brexit thrash...

EDIT: thx for the tip.. I can save some €€ ordering at ampmaker