5E9-A intensity pot not working

[idamay]

I'm building a 5E9-A tremolux and having significant trouble with the tremolo circuit. I can get a light tremolo effect that is consistent, footswitchable, and responds as it should to the speed knob, so it appears that the oscillator triode is working fine. however, The depth knob doesn't really control the depth at all. it does nothing for the first 3/4 of its swing and for the rest, it just raises the cathode voltage of the PI, thus taking away the volume from the amp.

Frankly, i don't totally understand how the arrangement of the depth knob is supposed to work as i have never seen one quite like it on any other amp.

The cathode follower triode has about 340v on the plate, 248v on the grid, and 250v on the cathode, and on the cathode of the PI, there's about 2.25v until i get up to about 3 o'clock on the depth, where it starts heading up to 4.5 with the depth all the way up

[PRR]

Welcome.

http://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Tremolux-5E9A-Schematic.pdf

Voltages around the PI, trem at min and trem at max. Compare to schematic (page 2). Your cathode follower is sitting 50V high, which may be OK, or may be a clue.

> i don't totally understand how

The cathode follower cathode is bopping up and down. If this bop is coupled into the PI cathode circuit, PI gain will bop up and down, more as the coupling is increased (coupling resistance turned from 250K to 71K). Or that's what's supposed to happen. Yes, the DC voltage shifts; that should be acceptable.

[idamay]

I'm in the midst of silkscreening the faceplate so i'll get those voltages when i get it reassembled.

One thing that confused me about the layout's voltages on the cathode follower is that is shows the grid (235v) at a higher voltage than the cathode (205v), it was my understanding that the grid should be negative with respect to the cathode in a cathode follower. Does this not have to be the case?

I see the cathode is quite high, but what could that mean? what could i do to change it?

I understand how the tremolo is supposed to shift the bias of the PI but i don't see how the high voltage on the cathode of the CF isn't going to make it down to the cathode of the PI and severely mess up the idle bias as it seems to be doing in my amp. I've heard that the depth knob can take a little volume from the amp when it's cranked, but in mine it's making it completely silent.

[sluckey]

One thing that confused me about the layout's voltages on the cathode follower is that is shows the grid (235v) at a higher voltage than the cathode (205v), it was my understanding that the grid should be negative with respect to the cathode in a cathode follower. Does this not have to be the case?

The grid will be negative with respect to the cathode, just as your measurements show in the original message. There have been many little errors discovered on the old original Fender schematics/layouts. I believe you have just discovered another one.

... i don't see how the high voltage on the cathode of the CF isn't going to make it down to the cathode of the PI and severely mess up the idle bias as it seems to be doing in my amp.

That dc voltage on the cathode of the CF goes through a voltage divider that consists of the 250K pot (with the 100K resistor) and the 1.5K resistor for the PI. That voltage divider knocks that dc voltage way down. I just calculated the voltage that would be present on the cathode of the PI using Fender's claimed 205v and 250K for the pot set to minimum and 71.4K with the pot set to maximum. My calculated voltages agree with your actual measured voltages.

Can you measure the amplitude of the tremolo signal present at pin 2 of the CF? A Fluke DVM can measure the RMS AC value of that trem signal. Or use a scope to measure the peak to peak voltage. I suspect the trem signal is just not as strong as it needs to be. Swap several 12AX7s into that trem tube socket.

[PRR]

> about 2.25v until i get up to about 3 o'clock on the depth, where it starts heading up to 4.5 with the depth all the way

[idamay]

Can you measure the amplitude of the tremolo signal present at pin 2 of the CF? A Fluke DVM can measure the RMS AC value of that trem signal. Or use a scope to measure the peak to peak voltage. I suspect the trem signal is just not as strong as it needs to be. Swap several 12AX7s into that trem tube socket.

Im having trouble getting a consistent reading on that pin, sometimes it goes up and down between 20 and 30v and sometimes it seems to be up around 40v

[idamay]

> about 2.25v until i get up to about 3 o'clock on the depth, where it starts heading up to 4.5 with the depth all the way

that was not the pin i was referring to. the one i was referring to was the cathode of the PI, not the LFO. on the cathode of the LFO, where those two voltages are written, i'm getting about 1.5v at min and actually less (.9v) at the max setting on the depth

[PRR]

> not the pin i was referring to

I was mistaken.

But looking again, the LFO cathode will not change with Depth pot setting. (That's what the cathode follower does: isolate the LFO from whatever happens around the Depth pot.) So I _now_ think the note was put on the drawing at the wrong tube.

[idamay]

yeah, that does seem odd. that being said, I am getting a reading on the LFO cathode that varies to some degree based on the position of the depth pot (.9-1.5v) do you think that is enough to be significant?

[HotBluePlates]

Would it be possible to get a high-res photo of that area of the amp?  Perhaps post to Imgur if too large to upload directly here.

I wonder if there could be a minor wiring error hiding in plain sight.

[PRR]

> LFO cathode that varies to some degree based on the position of the depth pot

That seemed "wrong" to me, but I was not sure, so I hung a fusebox and dug at the bat-pond waiting to see if others thought it was fishy.

I think HBP is seconding my doubts.

[shooter]

dug at the bat-pond

You don't have enough skeeters for your bats?

I am curious, what's a bat pond?  I have a small pond and some large browns, sadly all the small browns disappeared from the fungal? disease that wacked our little browns bad

[idamay]

I'm not sure if it's related or not, but i had a concern regarding B+ voltage in this amp. A problem i've noticed with this amp is that it doesn't seem to have the volume that I would expect from an amp in the 12-15W range. I'm considering the possibility that this and perhaps the trem issue could be symptoms of a low B+ voltage.

The readings on the Layout are:
1st node: 395v
2nd node 370v
3rd node 290v

While my amp reads
1st node: 340v
2nd node 320v
3rd node 285v

Granted, they're still technically within 20% but it seems low. Tell me if I'm making a fuss over nothing.

My transformer was sourced from an old hammond organ, and the secondary is labeled 320v on the schematic for the organ; it reads about 313v AC so that seems reasonable. I also tried replacing the used 5u4 rectifier with a new 5y3 (all i had) and the voltage decreased slightly as i would expect when swapping a good 5u4 with a 5y3.

I don't know exactly how much DC to expect out of a given AC secondary but the 5G9 schematic shows 370VDC from a 300VAC secondary (with a 5u4), so it seems like I should be getting more B+.

could there be a partial short somewhere? maybe the power tubes? I notice the first two nodes are the only ones with the issue.

[shooter]

maybe the power tubes?

probably need some more #'s;

What's the voltage on the Power tubes cathodes, with that and plate volts you can determine current flow and impedance based on your B+ and I. Then calc Power, or measure at the speaker and calc to see how close to your target 10-12W really is

[idamay]

the voltage on the cathodes is 15.94v

i calculated the plate dissipation to be 13 watts, which i understand to be above recommended spec. However, i'm shaky on the relationship between plate dissipation and output power. the amp sounds too quiet regardless and I don't have the equipment to measure output power.

Also, that 2nd node b+ voltage that feeds the cathode follower is 50v low, could that be responsible for my trem issue?

[shooter]

the amp sounds too quiet regardless and I don't have the equipment to measure output power.

monitor that tap while the amp is just idling, maybe 10-15minutes, does it drop slowly?
I'll try and look closer at the schematic, but works gonna get in the way for now.  There is probably a point where you can just "disconnect" the trem and see if your volume comes back.

you can use a steady signal at the input, adjust volume till you start to hear distortion, measure the AC volts at the speaker (in RMS), or peak to peak and calc RMS, then use ohms law and speaker value to calc power @ speaker.

[idamay]

monitor that tap while the amp is just idling, maybe 10-15minutes, does it drop slowly?

you mean that B+ tap? Apart from a small spike right when I flip the standby switch it stays consistent.

As for the output, I couldn't get a reading past about 5v (3W) or so with a guitar, so i tried playing a 1000 hertz signal from my phone with which i was able to dial it up to about 11v (15W). I'm not sure how accurate either of those are as the guitar is not a constant signal, and the phone has a higher amplitude to begin with.

After that, I tried disconnecting the tremolo by disconnecting the line from the depth pot to the PI cathode as well as the b+ to the trem tube. That gave me quite a bit of power back, and i was able to get a reading from the output that was more in the 15w range with a guitar at the input.

The B+ voltages were the same whether the trem was connected or not. does this mean something's hogging current in the trem circuit?

I used the power transformer from a hammond AO-29. I discerned that it would work in a tremolux based on the AO-29 having 1x12AX7, 2x12AU7, 1x6BA6, 2x6AU6, 2x6C4, and dual 6V6's. That seems like it must take way more current than what I'm using here (plus the thing is massive)

[shooter]

The B+ voltages were the same

DC volts and AC signal, co-exist, so if the DC volts is good and constant, then it's probably something eating the AC signal?

[PRR]

> if the DC volts is good

Is it? I'd like to see all the PI and power stage voltages in one list, with and without trem.

The real funny thing is that the trem *switch* should not affect the DC voltages at all. If it does, something is wired wrong.

[idamay]

Okay, I think the severe decrease in volume (my 3w measurement) was somewhat the result of a bad phase inverter tube, I was getting just 9v on one of it's plates so i switched it out and came up with a more reasonable voltage.

That was a brand new tube, could something be killing them?

That being said, the trem still seems to rob power to a small extent, but even with it disconnected i was hardly getting above 10W of cleanish output power

Here are the voltages going from left to right on the layout (minus the repeats of the third B+ tap). note that when i disconnected the tremolo, I cut both the line from the B+ and the line from the Cathode follower


  Power Amp Cathode
on layout: 235v (surely a mistake)
trem connected: 15.5
trem disconnected: 15.5

  first power supply tap:
on layout: 395v
trem connected: 337
trem disconnected: 337

  Second power supply tap:
on layout: 370
trem connected: 317
trem disconnected: 317

  Third Power supply tap:
on layout: 290
trem connected: 282
trem disconnected: 282

  Cathode of trem tube (pin8)
on layout: 2.1v@min depth, 4.5v@max
trem connected: 1.2v@min depth, .7v@max
trem disconnected: 0

  Plate (LFO) and grid (CF) of trem tube (pins2&6)
on layout: 235
trem connected: 145v@min depth, 215v@max
trem disconnected:0

  Cathode of trem CF (pin3)
on layout: 205
trem connected: 145v@min depth, 215v@max
trem disconnected:0

  trem jack
on layout: 25
trem connected: 18-25
trem disconnected:0

  PI plate (pin6)
on layout: 230
trem connected: 255
trem disconnected: 219

  PI plate (pin1)
on layout: 230
trem connected: 247
trem disconnected: 204

  PI Cathode (pins8&3)
on layout: 2.4
trem connected: 1.7@min depth, 2.8@max
trem disconnected: .9

  Preamp Plate: (pin6)
on layout: 150
trem connected: 185
trem disconnected: 185

  Preamp Plate: (pin1)
on layout: 150
trem connected: 194
trem disconnected: 194

  Preamp Cathode (pins8&3)
on layout: 2.4
trem connected: 1.65
trem disconnected: 1.65

Most of these measurements were taken with the tremolo turned off via the footswitch (except on the switch jack) as the voltages around the trem would swing making it hard to get a reading with my digital meter.

The B+ going to the power tube plates and screens seems low and i'm wondering if that could be contributing to my small lack of power.

The grid and the cathode of the cathode follower seem to have the same voltage, not sure if that's a clue or not

[shooter]

grid and the cathode of the cathode follower

there was a thread that talked about not being able to measure grids of CF because it would un-bias the tube.

the trem still seems to rob power

I'm not a trem-expert so your voltage readings might be ok, it just seems an AX7 shouldn't drag B+ down 60 volts

getting above 10W of cleanish output power

I wouldn't expect much more clean

[ac427v]

I'm enjoying and learning from your Tremolux experience. Someday I gotta to do that one! A few random observations:
The layout diagram may have a faint decimal point on the power tube cathode voltage (23.5 volts). That would clear up the discrepancy about your reading.
If your wiring is correct, you could boost voltage to the entire amp by using a 5AR4 rectifier. That would provide a slight boost in clean power but may lose some of the sweet distortion.
A 12AY7 is the specified V1 preamp tube. Does your build use that tube? I ask because using a 12AX7 will cause higher voltage on the plate as your build seems to have. It will also decrease apparent clean headroom.
--Craig

[sluckey]

The grid and the cathode of the cathode follower seem to have the same voltage, not sure if that's a clue or not

That's how it should be. Well, actually the grid should be 1 or 2 volts less than the cathode.

Does the tremolo perform satisfactorily now? Are you sure all components are correct values and you don't have a wiring error? Why haven't you posted some hi rez pics?

[idamay]

I'm enjoying and learning from your Tremolux experience. Someday I gotta to do that one! A few random observations:
The layout diagram may have a faint decimal point on the power tube cathode voltage (23.5 volts). That would clear up the discrepancy about your reading.
If your wiring is correct, you could boost voltage to the entire amp by using a 5AR4 rectifier. That would provide a slight boost in clean power but may lose some of the sweet distortion.
A 12AY7 is the specified V1 preamp tube. Does your build use that tube? I ask because using a 12AX7 will cause higher voltage on the plate as your build seems to have. It will also decrease apparent clean headroom.
--Craig

Good point about the decimal, i still can't tell though

I may try a 5ar4, but for now i was just wondering if the rectified voltage seemed low given the 315vrms winding and the stock 5u4. I think fender used a transformer with a winding of similar voltage so i was wondering why they seem to have been able to get 395vDC and me so much less

I have been using a 12AY7 as well

[idamay]

The grid and the cathode of the cathode follower seem to have the same voltage, not sure if that's a clue or not

That's how it should be. Well, actually the grid should be 1 or 2 volts less than the cathode.

Does the tremolo perform satisfactorily now? Are you sure all components are correct values and you don't have a wiring error? Why haven't you posted some hi rez pics?

Yeah, the grid was 1or2 volts less, but last time i checked it i think they read the same. i may have made a mistake though, everything seems to behave the same as it did before

The intensity pot is still not working correctly. the tremolo speed changes as it should with the speed control, and it can be turned on and off with the footswitch, but the intensity pot doesn't really change anything about the depth of the effect apart from maybe at the very last bit of the turn at which point the PI is biased extremely quiet and just sort of "coughs" out the notes anyway.

I've been checking thoroughly for a wiring error and have yet to find one, and though i can never totally rule out those types of mistakes, it just seems like it's too close to working properly for something to be wired up wrong.

This is a bit of a budget build and i'm using a recycled terminal board so i had to make some small changes to the layout. that and the fact that i haven't followed the color code made me assume that photos wouldn't be that helpful, but i can post some if you want.

[sluckey]

the fact that i haven't followed the color code

Huh? Surely you followed the resistor color code. That's very important.

I listened to several YouTube demonstrations of 5E9-As and the tremolo worked very well and had plenty of intensity.

[idamay]

lol! no, no, no, i meant for the wires. i noticed a number of fender layouts had particular colors for certain leads. i used my own colors based on what made sense to me at the time (and what i had).

[idamay]

right now, chief among my concerns is my B+ Voltage. My power transformer is giving me 310ish VAC, and i'm using a 5u4 rectifier. my research suggests that the original PT as well as modern replacements are in the same neighborhood voltage-wise, so why can't I get close to that 395VDC specified in the layout? is something drawing too much current?

[sluckey]

Pull the output tubes. How much B+ do you have now?

[idamay]

wow, 445VDC without the output tubes

[sluckey]

Maybe your output tubes are running really hot and sucking too much juice from the power supply. With tubes back in measure both plate voltages and cathode voltage. Also measure cathode resistor. Post these values.

Maybe your Hammond donor PT is too wimpy or maybe faulty. Which Hammond amp did the PT come from?

I really don't think the B+ is the cause of your tremolo issue.

Where are those hi-rez pics?

[idamay]

i increased the cathode resistance a little and now i'm getting 357v on the first filter cap. 348v on both 6V6 plates. 21v on the cathode. 267ohm cathode resistor.

[idamay]

The PT is from a Hammond A0-29 amp. I believe that's from a M3 organ.

[idamay]

more

[idamay]

...

[idamay]

...

[idamay]

note that I had the trem disconnected at the time most of these were taken, thus there are two wires floating about.

[sluckey]

The PT is from a Hammond A0-29 amp. I believe that's from a M3 organ.

I looked at the AO-29 schematics. I believe that PT is working just fine.

The pics didn't reveal any "aha!" problems. I would suggest cleaning up that cone board. There is a lot of flux around the cones that may be causing resistance/voltage leakage between cones. If there is leakage it can cause a variety of unpredictable problems. The board is easy to clean. Just use mineral spirits and a variety of small brushes, even a toothbrush. I like acid brushes because they are cheap and work well. I usually use one with 1" long bristles and another that I have trimmed the bristles to about 1/2". The shorter bristles are stiffer and work well on stubborn flus blobs. The mineral spirits will soften and dissolve the flux making it easy to brush off the board. When the board is clean you will need to clean up the splatters from the bottom of the chassis. This is easier than cleaning the board.

You should be able to clean the board so it looks similar to this one...

     http://sluckeyamps.com/RCA/RCA_07.JPG