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Newbie question- Ampeg B15N

#81
mcrracer said:
Great job for a first build. The fact that it actually works without a lot of hum and hiss is a testament to a good job. One question though... Your final wiring does not really look like that picture does it? If it does I would neaten that up a bit. It could be a problem down the road. But if it works , maybe leave it alone.
Click to expand...

Actually the wiring is a little better, but not much, it is color coded and I have been in it so much i know what every wire does, but I was doing layout on the fly and doing component swapping so i consciously left room between wires so i could get the soldering iron in an out easily.
But I will do a clean up... I'll do some before and after pics as well ;)
 
#82
Great, I was not criticizing. I build tube amps and have been for some time and I know from experience what sloppy wiring will do to an otherwise great build. Generally you want your wire runs to be as short as possible, not running parallel to other wires and if they have to cross another wire do it as right angles. Again good job. I am considering a couple different lower powered bass amp build including an B15NC.
 
#83
mcrracer said:
Great, I was not criticizing. I build tube amps and have been for some time and I know from experience what sloppy wiring will do to an otherwise great build. Generally you want your wire runs to be as short as possible, not running parallel to other wires and if they have to cross another wire do it as right angles. Again good job. I am considering a couple different lower powered bass amp build including an B15NC.
Click to expand...

Thanks for the tips, there's lots of 'conventional wisdom' about wiring out there some of it contradictory.

Yeah I thought about building the original B15 but this was for my son and he already had 30watt amp and needed something bigger to do larger clubs and play with louder bands. That's why I attempted to build a classic tone into a higher power amp. This rig is definitely loud.
 
#84
Was still fighting hum and random hiss and came across
some info on fliptops.net that recommended against using
Sovtek 6SL7s in Ampeg circuits. So I just bought a set
of NOS JAN-6188s and ditched the Sovtek tubes.
What a difference !!!
6188.jpg

And then mated it to a slightly used
Ampeg SVT-410HLF Classic Series Bass Cabinet

A very nice rumble
cab.jpg
 
#86
Since my son plays both guitar and Bass, I decided to see what I could find that would make this amp be slightly more guitar friendly.

Since most guitar amps use 12AX7 on the pre-amp side i looked at how hard it would be to convert from 6SL7 to 12AX7 and then I found these on eBay from a guy in china.

6SL7to12AX7-socket.jpg


These adapters let you use a 12AX7 in your B15 instead of 6SL7 Without any rewiring !! pretty cool. The sound when used for guitar seems a bit crisper ( or at least my 15 your old son claims that) also has a little less hum. The B15 uses 2 6SL7s, one for preamp and one for splitter, I tried switching both out for 12AX7s using those adapters but the sound seemed less full somehow using the 12AX7 on the splitter side. So left that one as is. So now when my son use the amp for guitar he swaps the pre-amp 6SL7(actually JAN-6188) for 12AX7 and switches back for use with his Bass.

12AX7adapted.jpg

This should work with any B15 or circuit that use 6SL7s.
 
#88
mccracer:

Yes, I'm still working on the amp but the project's had to go on the backburner numerous times the past 2 yrs. But last Sat. I finished the double baffle cab and loaded the JBL D130 that I reconed into it and tried it out for the first time w/ a bass guitar and it sounds kick ass! Still have to build a head for the electronics and figure out a way to bring down the plate voltages. More details later. danfishinman: your 100W head looks fantastic!
 
#90
Gee- I wished I had seen that notice about Sovtek 6SL7's about 2 wks. ago: I bought some and they hum! I guess I could use one in the PI but meanwhile the NOS are working just fine. I bought a Sovtek 5Y3 a few years ago and later found out that they were another tube type that had been re labeled and it's possible that it helped caused the death burn up a vintage OT. I probably won't buy Sovteks in the future.
 
#91
slavax said:
Gee- I wished I had seen that notice about Sovtek 6SL7's about 2 wks. ago: I bought some and they hum! I guess I could use one in the PI but meanwhile the NOS are working just fine. I bought a Sovtek 5Y3 a few years ago and later found out that they were another tube type that had been re labeled and it's possible that it helped caused the death burn up a vintage OT. I probably won't buy Sovteks in the future.
Click to expand...
I wish I had seen that note from fliptops earlier too. ;)

I'm not sure I'd condemn all sovtek tubes but definitely won't use their 6sl7s.
BTW I'm using Svetlana 6L6GCs on the power stage.
 
#92
Details on my B15 project:

Only one channel
Added a Fender- style bias adjust knob
" bias check resistors
" a variable negative feedback knob
" a Baxandall James stack w/ frequency shift (zugster link earlier in this thead.)
Made a solid- state plug- in rectifier but haven't used it b/c my plate voltages are too high. Right now I'm using a 5U4GB instead of a 5AR4. I might try building the Vintage Voltage project from Geofex; I've got some other equipment that could benefit from that.
 
#93
Have you used a 5ar4 in it? If so, what did you think vs the 5u4gb? I've got a 5u4gb in my Super...i should give it a shot in the B-15. I can plug one in without modding the amp, right?
 
#94
I did use the 5AR4 in it at first but my plate voltages were way too high - like 520 V. A friend suggested putting in the 5U4GB to drop the power supply voltage. (I've got a Leslie cabinet that uses them.) The 5AR4 drops about 17 V and the 5U4GB drops about 50- 55V. I believe the 5AR4 is actually a superior tube. You can sub the 5U4 w/o modification but if your B15 works fine there's no reason to.
 
#95
slavax said:
I did use the 5AR4 in it at first but my plate voltages were way too high - like 520 V. A friend suggested putting in the 5U4GB to drop the power supply voltage. (I've got a Leslie cabinet that uses them.) The 5AR4 drops about 17 V and the 5U4GB drops about 50- 55V. I believe the 5AR4 is actually a superior tube. You can sub the 5U4 w/o modification but if your B15 works fine there's no reason to.
Click to expand...
Ya, after I posted that, I decided to ask about it in the Portaflex Club thread, and beans on toast recommended against it, basically. So I'll stick with what I have. Just spitballing, you know?
 
#96
slavax said:
I did use the 5AR4 in it at first but my plate voltages were way too high - like 520 V. A friend suggested putting in the 5U4GB to drop the power supply voltage. (I've got a Leslie cabinet that uses them.) The 5AR4 drops about 17 V and the 5U4GB drops about 50- 55V. I believe the 5AR4 is actually a superior tube. You can sub the 5U4 w/o modification but if your B15 works fine there's no reason to.
Click to expand...

Sounds like a good plan to swap out the 5AR4 in your case. If you are using a modern transformer that has at least a 3A current capacity on the heater tap, no problem using a 5U4GB. I don't recommend doing this with a vintage transformer because of the extra stress the higher current draw would cause.

Measurements from my B-15N with a 5AR4 put the voltage on the plate (pin-3 on the 6L6GC) at around 420 volts with AC line voltage of 117VAC. My NA was designed to run about 440V at the plates with a solid state rectifier. So 520V is a bit high but the 6L6GC can take it despite what the data sheets say.

There are other ways of lowering your B+ voltage. You can add a dropping resistor on each leg of the high voltage secondary, or add a zener diode on the center tap of the HV secondary. Weber sells zener kits for doing this. Some areas have higher (125VAC) line voltages that raise the PT secondary voltages. If you don't have a variac, you can lower it with a cost effective bucking transformer that steps the line voltage down to something closer to 117 VAC.
 
#97
Yeah, our line voltage gets up to around 121-122. I've looked at the Weber kits nut I'm so tight on space I don't think I've got a good, safe place to stick it. I'm think the Geofex Vintage Voltage is the way to go. Long story short: I should have tested the transformer before I started clipping wires.
 
#98
slavax said:
Yeah, our line voltage gets up to around 121-122. I've looked at the Weber kits nut I'm so tight on space I don't think I've got a good, safe place to stick it. I'm think the Geofex Vintage Voltage is the way to go. Long story short: I should have tested the transformer before I started clipping wires.
Click to expand...

Over voltage issues are very common in amp building. People wind up adopting all kinds of solutions to fix these problems.

Sometimes it's better just to chalk it up to a learning experience and get another transformer that will do the job properly.
 

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