Questions on a build of a modified 1968 Ampeg B-15 N.

[J Luth]

1mV ??? Is this a typo?

Yes 100mV



The BIG TOE!!? I've never heard of anyone doing that. Must hurt like hell. Well wishes and a speedy recovery.

Thanks

The story is too long but I did protect the Les Paul Studio from certain disaster from the concrete floor.
I sacrificed both knees, my left toe and my right thumb. Only damage to the guitar was one tuner broke apart, not a scratch, dent or ding except on me. I managed to find all the parts and with a bit of persuasion and a small drill press vise I got it back together enough so it works. Told the owner what happened, he is OK with it until I get a replacement.

Fix was so good that if I wanted be a jerk, I could have put it together and not said anything. He probably would not have seen it for a long time if ever. But that is not my style, if I screw up I own up to it.

[Chuck H]

Ah. Yeah. I probably would have done it for a customers guitar too. My own guitar? I dunno. It would depend which one I guess. But it's great that your effort actually worked, in a sense. It's easy to imagine a case where you try to save the guitar, get busted up and lose control of the guitar anyway. Hard to call it a success but you can't call it a failure I guess.

[Helmholtz]

FWIW, Dave Funk mentions that the 5F8 Twin put out 60W, so I guessed right.
I think Leo always chose a PT that would not allow to overpower the speakers.

[Chuck H]

FWIW, Dave Funk mentions that the 5F8 Twin put out 60W, so I guessed right.
I think Leo always chose a PT that would not allow to overpower the speakers.

That's a book I don't have and probably should. Christmas is coming. I'll tell the wife

[Helmholtz]

That's a book I don't have and probably should. Christmas is coming. I'll tell the wife

Definitely!
It's one of my most used books since decades, mainly because of the comprehensive collection of Fender schematics.

[nosaj]

https://www.amazon.com/Dave-Funks-Tu.../dp/1500115185
nosaj

[J Luth]

I don't want to get side tracked with the tweed Twin, it was just an example of a real schematic showing 4 power tubes on a single rectifier tube.

The B-15N is a 25W amp.(edit: The 'NF' version in the schematic from the first post is rated 30W). Even with double the PT power capability, we are still only in the 60W range.

J Luth , you said the amp is working with a SS rectifier. What is the measured power output of the amp?

Usable power output with SS rectifier, going from memory, I can't work on it right now is approx 75 or 85 watts just before clipping with 4 6l6GC

[J Luth]

The high power tweed Twins are supposed to put out 80W. I have never tested myself so can not guarantee that. Fender spec'd them for 85W.


It's all about the power transformer, you have not mentioned what it is.

I took a careful hobble down the basement stairs, that was a bit sketchy with this boot on my foot, to get the power trans info. The info I was given when I got it was wrong on the 5V rectifier tap. The tag said 5V 3A. I decided to look up the trans and found it is out of an Eico ST70.
I found these specs 360v - 360v (720 CT) 5V 2A NOT 5V 3A, 2 - 6.3V 3.5A EA FILAMENT 80V BIAS
The ST 70 used 3 X 12AX7, 2 X 12DW7, 2 X 6SN7GTB, 4 X 7591, 1 GZ34.
What I have uses 2 X 6SL7, 4 X 6L6GC OR 4 X 7581A and a tube rectifier or SS rectifier
I don't see why the 5AR4/GZ34 when put in is lighting up like a Christmas tree when pushed a bit.
Well probably wont be using a 5U4 seeing as how it wants 3 amps.
Going to see if I can get the 5ar4 to work. And also contact the guy I got the transformer from and see if he has something else of a 5V 3 or 4 amp filament trans I can add.
Here's the trans with the numbers. That picture is not mine but it is identical.

[J Luth]

Don't know when I will get back to this.
More than just a toe problem, the whole foot is messed up. Wont need surgery but will take some time to heal.

[Chuck H]

Don't know when I will get back to this.
More than just a toe problem, the whole foot is messed up. Wont need surgery but will take some time to heal.

Need a "don't like" tab for this one. Seems like there's a lot of this around lately.?. So many people in my own circle have recent and difficult maladies to cope with.

Best wishes for an easy recovery.

[J Luth]

Need a "don't like" tab for this one. Seems like there's a lot of this around lately.?. So many people in my own circle have recent and difficult maladies to cope with.

Best wishes for an easy recovery.

Thanks Chuck H.

I wish this was the only problem.

It's been a bit of a wild ride over the last 3 years, some serious issues, but hopefully it will all be behind me soon. Wont know till the end of January.

But it wont stop me, might slow me down a bit though.

Once the foot is better I go back to normal.

Getting old is a trip

[J Luth]

Boot is finally off. The foot and toe are still a bit sore and still swollen, YIKES, I did this back on Dec. 1st.

As far as the amp goes, it's going to stay the way it is for now with regards to the rectifier. It works fine with SS rectifier or with a 5U4 plus I don't have any more 5AR4 tubes to try. Added a small a 5V - 4A filament transformer to handle 5U4 and possibly others. The power trans only has 2A tap.

Change again
Going to stay with the tone stack below.