First Build

[GregS]

Hi, I'm new to the forum and about to start my first amplifier build. I've decided to build an Ampeg Portaflex clone. I think this will get the tone I'm looking for and also will be a good first project because of it's relative simplicity. My only major concern is that it won't be loud enough for rehearsing with the band and playing gigs.

I'm wondering if I could easily double the output of the power amp section by adding an additional set of output tubes. If I understand correctly each bank of tubes would be connected in parallel with each other (i.e. the pins of the extra tube I'd be adding are connected directly to the corresponding pins of the existing tube on the same side). Correct? Would I need to use an output transformer with different specs? Any other changes in the circuitry?

The goal would be to retain the tone and character of the original design and simply make it louder.

I have a high school level electronics background and have only been learning about amplifier circuitry the past month or so. For this reason I'm wondering if I might be better off sticking with the existing plans for my first build instead of attempting this power enhancement. Thoughts?

Thanks,

Greg

[Enzo]

Not that simple. Yes, the two new tubes would be more or less in parallel with the existing ones. The output transformer would need to be replaced with one for the purpose, and power has to come from somewhere, and in the case of an amplifier, that somewhere is the power transformer. You'd need a new one of those. The voltages might want to be a little higher, maybe not.

Portaflex isn;t very specific, what amp model are you looking at?

The single largest contributor to the sound is the speaker. To get the original tone and character would include making a similar cab and using a similar speaker.

Double the power for louder? Power is not so directly connceted to loudness. DOuble the power, and the volume increases only 3db. That is not much. Ad a reference, on many Fender amps - and others - there are two inoput jacks on an amp. One is a little louder than the other. Nowdays they like to call them active and passive. REgardless of the name, the typical Fender dual input jacks are 6db apart. The loud one is only 6db louder. That hopefully will put that 3db increase in perspective.

REmember the speaker I mentioned? Speakers have an efficiency rating along with the power rating. it is in decibels. A typical speaker might have a 97db rating. It refers to the loudness of a test signal; when one watt is applied and the loudness is measured one meter away. It is a way to compare speakers. The more efficient the speaker is, the louer it will be for a given power level.

A 100db speaker will therefore be 3db louder - all other things being the same - than a 97db speaker. These are the same 3db you could have got by doubling the amp power.

My point is that instead of doubling the amp power, if you get a speaker that is 3db more efficient, you will get the same loudness increase.

Of course, you might do both, but just like finding change in your couch cushions, there is a limit to what you can get.


Not loud enough for gigs? What is the PA system like? RUn your bass through the PA, and use the amp just as a stage monitor.

COnsider building a preamp, then using a commercial power amp for volume. REmember, a 100 watt screaming guitar amp is freaking loud. 100 watts of bass is not much. A 1000 watt bass amp is not about screaming loud, it is about making the sound effortless through the speakers, it is about allowing peaks to come through cleanly. Especially so if you pop and slap and otherwise invoke a lot of acrobatic play.

Twice power is only 3db louder. To get twice as loud, you need 10 times the power.

[tubeswell]

My measely two cents worth is that with a first amp it is a good idea to start with something real basic and tried many times over like a tweed champ, tweed princeton or tweed deluxe where there is alot of commonly available help from those who have had similar experiences, and that way when you need to troubleshoot stuff, its relatively easy (tho' not always absolutely easy) to get to the bottom of it. Whereas if you start with something more ambitious and a bit more off the beaten track (and I'm not saying Ampegs are off the beaten track - its just that there's probably been less of them DIY'd than the other types I've suggested), you may well be more likely to get frustrated and discouraged if you can't quite get things the way you imagined they should be when you started out. (Speaking from my own expeawience)

(But don't let that stop you from trying what you want).

[txstrat]

Are you talking about the Ampeg B-15 N Portaflex bass combo amp?
If so I might can help with some information since I built one of those with a 80 - 100w power section of 4 6L6GC for my bands bass player. Enzo is right 100w is not that loud for bass but if you have the right speaker and cabinet it might cut throught the mix when you crank it. That's what our bass player does and the amp sounds fantastic (even with the poweramp getting softly into saturation). It's ok for small club gigs.
Are you planing to build the amp from scratch? Do you already have the parts you need?

Matt

[GregS]

Thanks for the replies and advice.

The amp project I'm working from is Kevin O'Connor's version of the Portaflex in "The Ultimate Tone 3". I haven't ordered parts yet which is why I'm tyring to decide now how I want to do this.

I was concerned about straying from the beaten path and getting bad results and getting discouraged. I guess your first build isn't the best time to experiment.

Not loud enough for gigs? What is the PA system like? RUn your bass through the PA, and use the amp just as a stage monitor.

Presently, for gigs I already do this anyway so you're right - it shouldn't be an issue.

It sounds to me like I should stick with the original plan from the project book and focus my attention on speaker and cab selection instead. Of course, information on how to beef up the power section would still be of interest to me for a future build.

Thanks a lot for the suggestions and advice. This has been very helpful. Much appreciated.

Greg

[corworld]

Have you played through an actual B-15 Portaflex? If you have you know the limits it has as far a clean gain. I built an B-18 amp using a pair of 7027s and a very large cab with a 1x15. It has held up with drummers in a smaller room but I still don't turn it up past 12 o'clock until I want a lot of dirt in the sound. It is great for rehearsing and studio use which is why I built it in the first place.

Just be honest with yourself about what you need in terms of an amp and you will be fine.

[GregS]

No, I haven't played through a Portaflex before. If it turns out to be not loud enough or not enough headroom for playing with the band then I can always use a practice amp for at home which I don't already have. A lot of my motivation for this is the fun of building an amp. If it also works for me in a practical way then that is even better.