I heard it was the Marketing Dept. at Marshall hacking the Youtube site and removing the clip! LOL!
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Official Ampeg Portaflex Club
- Thread starter JimmyM
- Start date
I found it!
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SO 40 years from now, I guess I'm going to need to plan to replace the caps in my 20T.
I don't know, modern capacitors last longer. I know that my amps are probably going to outlive me.
Well, didn't expect so quick responses.
Some thoughts: After hearing that Hendrix video. My Bass player will have to pry this thing from my dead and rotting fingers, and even then, I'll fight him for it.
Anyway. Thanks for the replies. So yeah, figured I'm gonna have to redo the Caps at a minimum. But working in my budget to get all the parts before I really start pulling this guy apart.
My 2nd big issue. Tolex. Grrrr. Out of stock everywhere. I was looking at adequate replacements, Almost placed an order and then stopped. I couldn't bear to put some "close enough" tolex on it. I'd rather have the ratty original tolex than not quite right stuff. I'll settle in for the long wait until someone decides to do an accurate reproduction again.
A couple more pics for viewing pleasure.
The broken fuse holder:
Tubes: Mis-Matched hodge podge
Inside Cab:
Yeah, lots of cleaning, lots of work. But, should be a labor of love.
Some thoughts: After hearing that Hendrix video. My Bass player will have to pry this thing from my dead and rotting fingers, and even then, I'll fight him for it.
Anyway. Thanks for the replies. So yeah, figured I'm gonna have to redo the Caps at a minimum. But working in my budget to get all the parts before I really start pulling this guy apart.
My 2nd big issue. Tolex. Grrrr. Out of stock everywhere. I was looking at adequate replacements, Almost placed an order and then stopped. I couldn't bear to put some "close enough" tolex on it. I'd rather have the ratty original tolex than not quite right stuff. I'll settle in for the long wait until someone decides to do an accurate reproduction again.
A couple more pics for viewing pleasure.
The broken fuse holder:
Tubes: Mis-Matched hodge podge
Inside Cab:
Yeah, lots of cleaning, lots of work. But, should be a labor of love.
Sounds like a great thread topic. "Will my amps outlive me?"
Small parts such as the four-pin male and female cabinet connectors are available from Fliptops Home of Parts for Ampeg Lovers. Restorations can run from getting the amp to work to the whole enchailada.
The blue check vinyl is rare and expensive when you can find it. A B-15 cab is not easy to recover because of alignment of the squares. Makes sense to clean it up first and see. THese amps clean up pretty well. Some details are in the TB portaflex wiki.
I wouldn't want to tempt fate.
A lot of bass players like to change their amps often so maybe it isn't an issue. I think that those of us that regularly use vintage amps are few and far between. Holding on to an instrument is more common. Maybe that's inherent in us.
And a couple more
TBH... i ordered the NOS fuse holder from fliptops. Guess I'm trying my hardest to stay original to the amp. Hoping it will outlive me also, but then again, some days I think my breakfast has a pretty good shot at outliving me.
TBH... i ordered the NOS fuse holder from fliptops. Guess I'm trying my hardest to stay original to the amp. Hoping it will outlive me also, but then again, some days I think my breakfast has a pretty good shot at outliving me.
That's cool...I get that. If Jess hadn't installed it himself, I probably would have done the NOS fuse holder for the same reason. And I'm sure I'd have broken it again by now
Thats a great article! Many thanks for a good read to break up the monotony of another day at work.
Thats a great article! Many thanks for a good read to break up the monotony of another day at work.
I find it to be a very good magazine. Many articles have links to videos.
And here is my tolex issue. Guess I'll have to take the fall back position of "It has character" lol. I'll start the teardown on Saturday to start cleaning the surface stuff, chrome, acrylic ampeg plate, etc. Then wait for the mail to start delivering parts. Guess it won't be an overnight job. HA!
And sorry for some of the quality of the pics.
And sorry for some of the quality of the pics.
That's what happens when you shred.
A lot of work can go into a cabinet repair. An example of an SB-12 cabinet restoration is in the wiki.
A lot of work can go into a cabinet repair. An example of an SB-12 cabinet restoration is in the wiki.
I’m building something along the lines of the H B-15 Ampeg: Heritage Series - B-15 in a 3U rack-mounted chassis with Hammond 374BX, 1650 PA and 159P transformers. I have built one amp before, a stereo EL84 amp similar to a Leak stereo 20.
My main question concerns the bias and standby switches. The schematic I have is the first production model of the amp, with separate standby and bias switches. See here for a picture of the chassis, see the 3 switches on the right:
However they changed this mid-production to a combined 3-position switch with cathode bias up, standby in the middle and fixed bias down. See this picture:
I assume the reason they did this is because some people flicked the bias switch whilst standby was off, which would have momentarily biased the output at 0v with respect to cathode and probably made a bang. Is this right? or did they do it for another safety reason?
Can I make the same switch circuit as them? Using an ON-OFF-ON 4PDT switch rated at 380VAC @10A like this:
Wobble Lever 4PDT Locking ON-OFF-ON 3 Position 12 Terminal Toggle Switch
I would wire the two halves of the switch like the two separate switches in the schematic, with two poles of the switch between the power transformer and the rectifier, and the other two poles switching the bias. Here's a drawing to show you what I mean
The only thing I’m not sure is, when the switch is moved to the centre ‘standby’ position, there is no HT going to the rectifier but might there be still be some HT on the valves for a moment or so? Doesn’t it take a moment for the HT to dissipate from the power supply after the power is disconnected? This whilst the 6L6 cathodes are not connected to anything (ground nor cathode bias). But that should be fine right, no current will flow through the valve. The 6L6 cathodes are disconnected from everything at the same time as the AC is pulled from the rectifier.
Alternatively, if you think there would be no problem with switching between cathode and fixed bias with the HT applied, I would be happy to do away with the standby switch and just have a DPDT bias switch in its place. With the 12 second warm up time with the GZ34 on my EL84 stereo amp I have had no issues without a standby switch.
My other planned modifications to the circuit are: moving the HT fuse to between the power transformer and standby switch, having only one input jack socket with a channel switch and a pad switch, a 120/230 mains voltage switch on the back, and a Jensen JT-DB-E balancing transformer and XLR out with ground lift switch for preamp out/power amp in as well as the jack socket they have on the schematic. Any help would be much appreciated!
My main question concerns the bias and standby switches. The schematic I have is the first production model of the amp, with separate standby and bias switches. See here for a picture of the chassis, see the 3 switches on the right:
However they changed this mid-production to a combined 3-position switch with cathode bias up, standby in the middle and fixed bias down. See this picture:
I assume the reason they did this is because some people flicked the bias switch whilst standby was off, which would have momentarily biased the output at 0v with respect to cathode and probably made a bang. Is this right? or did they do it for another safety reason?
Can I make the same switch circuit as them? Using an ON-OFF-ON 4PDT switch rated at 380VAC @10A like this:
Wobble Lever 4PDT Locking ON-OFF-ON 3 Position 12 Terminal Toggle Switch
I would wire the two halves of the switch like the two separate switches in the schematic, with two poles of the switch between the power transformer and the rectifier, and the other two poles switching the bias. Here's a drawing to show you what I mean
The only thing I’m not sure is, when the switch is moved to the centre ‘standby’ position, there is no HT going to the rectifier but might there be still be some HT on the valves for a moment or so? Doesn’t it take a moment for the HT to dissipate from the power supply after the power is disconnected? This whilst the 6L6 cathodes are not connected to anything (ground nor cathode bias). But that should be fine right, no current will flow through the valve. The 6L6 cathodes are disconnected from everything at the same time as the AC is pulled from the rectifier.
Alternatively, if you think there would be no problem with switching between cathode and fixed bias with the HT applied, I would be happy to do away with the standby switch and just have a DPDT bias switch in its place. With the 12 second warm up time with the GZ34 on my EL84 stereo amp I have had no issues without a standby switch.
My other planned modifications to the circuit are: moving the HT fuse to between the power transformer and standby switch, having only one input jack socket with a channel switch and a pad switch, a 120/230 mains voltage switch on the back, and a Jensen JT-DB-E balancing transformer and XLR out with ground lift switch for preamp out/power amp in as well as the jack socket they have on the schematic. Any help would be much appreciated!
Sounds like it will be a nice amp. I like the Jensen transformer on the pre-out.
Changes were made, including the standby switch configuration, to satisfy the EU regulators. There is a concern of switching from one bias to the other directly with the power applied. Normally you shut off the amp in order to switch from cathode to fixed bias. There is no reason why you would have to implement the three position switch.
As I recall, in the revision, they included a snubber circuit, a parallel resistor 470K 2W, like R41, and 0.047uF 630V capacitor, after the tube rectifier pin-8, between high voltage and ground. Between there and the power supply first 47uF cap is where the standby switch is. In place of fuse F2. It is not a dual switch on the high voltage as in the schematic that you posted. Makes it a little easier.
In switching to standby, there isn't time for the power supply to discharge C22 before going from cathode to fixed bias, but the high voltage is disconnected. In standby, the switch is open, in either bias mode, the switch will be closed, on-off-on. The switch that you selected can handle more than 380VAC because your current will be considerably lower.
Changes were made, including the standby switch configuration, to satisfy the EU regulators. There is a concern of switching from one bias to the other directly with the power applied. Normally you shut off the amp in order to switch from cathode to fixed bias. There is no reason why you would have to implement the three position switch.
As I recall, in the revision, they included a snubber circuit, a parallel resistor 470K 2W, like R41, and 0.047uF 630V capacitor, after the tube rectifier pin-8, between high voltage and ground. Between there and the power supply first 47uF cap is where the standby switch is. In place of fuse F2. It is not a dual switch on the high voltage as in the schematic that you posted. Makes it a little easier.
In switching to standby, there isn't time for the power supply to discharge C22 before going from cathode to fixed bias, but the high voltage is disconnected. In standby, the switch is open, in either bias mode, the switch will be closed, on-off-on. The switch that you selected can handle more than 380VAC because your current will be considerably lower.
Thank you for such a great helpful response!
I've been in the studio with a UK hB-15n so I just opened it up and had a look at the 3-pos switch. It looks like they've gone for a 3pdt on-off-on with one pole for the LED colour, one pole for the HT and one pole for the bias, either bypassing the cathode bias or fixed bias circuits to ground. So if I do this and incorporate your snubber circuit will it all be safe? Should I tap the bias from the 375V HT winding like on the schematic or use the 50v bias tap on my transformer?
I've been in the studio with a UK hB-15n so I just opened it up and had a look at the 3-pos switch. It looks like they've gone for a 3pdt on-off-on with one pole for the LED colour, one pole for the HT and one pole for the bias, either bypassing the cathode bias or fixed bias circuits to ground. So if I do this and incorporate your snubber circuit will it all be safe? Should I tap the bias from the 375V HT winding like on the schematic or use the 50v bias tap on my transformer?
You could use either to derive the bias voltage. You would have to modify the bias circuit to use the 50V tap. Instead of R45 to drop the voltage, you might want to use a voltage divider.
The Hammond transformer voltages may not be as per their spec sheet. It depends on your line voltage. The specs are at full load. So if you are not drawing the rated current, the voltages will be a bit higher.
The layout that you use is important in minimizing hum and noise. Care must be taken.
The Hammond transformer voltages may not be as per their spec sheet. It depends on your line voltage. The specs are at full load. So if you are not drawing the rated current, the voltages will be a bit higher.
The layout that you use is important in minimizing hum and noise. Care must be taken.
