Ampeg B-15N Tube Suggestions?

[Bodtker]

1966 Ampeg B15N
I received it with JJ power (6L6) and rectifier (GZ34), and sovtek 6SN7's.

The amp has no Mid control, mids are lacking for me and it is too 'Boomy' - I can't get enough low without being boomy. I cant get the mids up, even adjusting treb/bass both down and volume up. Tone seems good at low volume and gets progressively boomy with volume increase. It might be the 'boominess' overshadowing everything at volume.

I have 1 new TungSol 6SN7 - it sounds terrible to me in V1 (the channel I use), seems harsh.
I have tried a Weber 'Copper Cap' SS Rectifier - sounds terrible to me.

I don't know wether to focus on pre, rectifier, power, or all.
Your Suggestion - SED 6L6 - 'better bass response' - might that make it more boomy? I sort of have too much bass - or is it distorting.

[indianajo]

Anything built in 1966 that has electrolytic capacitors, they are dried up and low capacity. This will change frequency response. Capacitors take a soldering iron to change instead of tubes, but are more likely to be bad. Electrolytic caps are in aluminum cans, sometimes covered with cardboard or (later) plastic wrap, and have a plus or minus near one pin. If you are replacing them, buy replacements that have a voltage rating the same or up to 35% higher, and the same capacitance or 50% higher. Make sure you mark the board for which end is plus before you remove the old ones, if you get it backwards they leak slime. If you haven't soldered before, get a WP25 700 deg F iron or equivalent and wear safety glasses. If you have vertical can caps with tabs twisted in the board, you'll need a 130 W soldering pistol grip gun to remove them. Use scrap stranded wire dipped in flux (I use Oatey #5 paste from the hardware store) to soak up old solder before removing. Wash afterwards with a paper towel, this makes an acid. Use needle nose pliers and don't burn your fingers. Use rosin core solder 63/37 to put back (in the western hemisphere), R**** S***** is okay but Kester is a little better. In Europe you'll need a special high temp iron to intall the silver solder they require now over there.

[Bodtker]

Thanks for the pointers! Many of the 'big' caps look recent, but not all- so I think I will put this project on my list for sure. Do you recommend any specific brands? - I am sure this could be a book on it's own. Is there another board that would me more appropriate for discussing tube selection in amps like this? Thanks again.

[bob91343]

Don't agonize over brands. They are all pretty good these days. And the tubes, again they are all pretty much the same in spite of all the mythology.

Make sure all the components are good and it will work the way it was designed. If you decide you want to change that, let us know and maybe we can advise.

[indianajo]

American made capacitors before 1990 had a date code, YYWW where the y's were years and the w's were the number of the week 1-53. Anything before 85 year should be changed. I forgot to remind you that electrolytic caps on tube equipment can be deadly. Read the sticky thread at the top of the tube amplifer forum about tube safety before starting. In short, make a capacitor discharger with a 500-2000 ohm resistor in heat shrink with old meter probes soldered to the wires(600 v rated wire on plus), discharge your caps to ground, unplug the equipment, measure the capacitors below 20 V before even starting to touch things. No jewelry or watches, one hand at a time so electricity doesn't cross your heart. Read the whole thing. Working on tubes and NOT killing yourself is very gratifying, more dangerous than a motorcycle in traffic but not as loud. I just put 70 electrolytic capacitors in a Hammond organ last winter, really pepped up the sound (formerly weak and tinny), and no tubes needed changed. Rectifiers (GZ34) go bad first in most equipment. Capacitors come in different "life expectancy", a good supplier like Newark will tell you which are 500 hour (bad) which are 3000 hour at 105 deg C (very good). American made vishay spragues (atomlytics) don't have a life rating but in my experience are good for 25 years or more. Tall can caps (FP's) with the ground tabs are only available from specialty houses like tubesandmore.com, triodeelectronics.com, or the supplier whose banner is at the top of the tube forum.

[JIOREO]

I recently bought my first tube bass amp, a late 70's Ampeg B-15N. It's in VGC w/light use over those years (church on Sundays!) and even has it's orig Magnovox tubes. After reading indianjo's take on re-capping, I'm wondering if it is a given that I re-cap it w/o exception as it is a 40+yr old amp, even if it sounds good as is. But, if there is more of a 'don't fix it if it isn't broke' consideration, then what are the signs I should be looking for that it needs re-capping? I want to learn more about the care and maintenance of this beast to keep it sounding its best. Any input would be appreciated.

[indianajo]

If you like the sound, fine. A lightly used unit might not have leaked much of the slime (electrolyte) out. However, the rubber in the seals of the electrolytic caps is x years old (2010 -19yy of the cap date code), and if you have looked at historic tires or windshield wipers, historic rubber is dirt on a stick. So use will make it leak. Dry electrolytic caps in power circuits can explode blowing conductive slime and aluminum foil all over everything, so do what you want. You are warned.
Of my two 1968 organs, one motor capactor (electrolytic) burne out in 97, burning the insulation off the 120 vac wiring before the house breaker blew. (Dealer service replaced the cap, and a couple more in the power chassis, but not the burned wire). My second 1968 organ was working when I bought it, all on original caps. The motor cap was sitting in a puddle of it's own slime (ie it is a bomb waiting to burst). The rubber power cord is also original, and terribly cracked and dangerous. Deadlined on purchase, cap is purchased and waiting for fall rains to end car/roof repair season.
I've got a PAS2 preamp with two original 1961 tubes (12AX7) pretty heavily used 61-80 and again this year. The rectifier tube has been replaced twice. My two 1968 organs, one has all original tubes, one has 2 of 26 replaced, probably because the repairman or church was too cheap to replace the electrolytic caps causing the weak volume. (1 power amp tube, one rectifier). Rectifier and power tubes can wear out, especially if overdriven in guitar amps. My ST70 power amp has worn out the rectifier (5AR4) and power output tubes (6CA7) twice in the 42 years I've owned it. TeeVee's were much harder on tubes than Hammond organs and Dynakit amps. I changed a lot of tubes in my mother's 1954 Philco B&W TV before she retired it in 1972 with a Sony Trimetron color set.

[indianajo]

A completely original amp may have some value as an antique. Antiques are not supposed to be restored. If you ever think of selling your amp at a big markup later, put your original Magnavox tubes, and any capacitors you replace, away for the next guy. Buy some Sovtek or Harmony tubes to use. The caps can be gutted and refitted with new innards by specialists, leaving the cans with the original production date. Not my hobby, but it might be yours.
Your caps might sound good, because at church they never used it enough to heat it up and boil the water off. That is probably the story on my second, working original, organ. If you never intend to have a 3 hour rehearsal,fine. Caps that explode tend to be big, with voltageXcapacitance (in UF) (uf now was mf in 1970) bigger than, maybe, 5000? Smaller caps tend to blow the end off and hiss as the slime leaks out.
Enjoy your new instrument.

[JIOREO]

Wow Bob wow! I ordered a set of tubes as a back-up, but after reading what could happen I think I'll replace the tubes and box the originals for their collector value and for safe use of the amp. I'm a player, not a collector so my priority is using the amp. I appreciate your insight and will look into getting it re-capped, saving the working originals for later as well. There are tube guru's here in the SF Bay Area that specialize in such. I plan on learning more but it sounds like it would be accomplished best in the hands of experts. Tube amps are a whole universe aren't they? Thanks again for sharing your working knowledge.

[fretts]

Maybe you don't like the speaker? It could be old & tired or just not to your liking. Have you tried the amp with a different speaker... You may possibly get what you are after by picking a speaker that's strong where you like it.