5F1 Champ DIY: No sound (Tube/Transformer)

[adammerah]

Hey guys this is my first time doing this, and my second time building a fender tweed tube amp (first one was a 5F6A 4x10 Bassman, worked perfectly).

I plugged it in last night (5F1 Champ) and was a little confused about the AC line wiring. So i plugged it in the first time and blew the HOME electrical fuse, not the amp fuse. Did that about 2 more times, (blowing the home fusebox), rearranged the wires, correctly, and then voila, heater wires are on (light) and 12AX7 is warming up. But no sound, none at all, and the rectifier (5Y3GT) and power tubes (6V6GT) are not warming up (no glow). I figured out that my dumb self switched the 5Y3GT and 6V6GT tubes, so i switched them back and the rectifier (5Y3GT) is glowing, 12AX7 is glowing but the power tube isnt. I am wondering with the voltages that the tube must have seen, could it have blown the tube? is replacement necessary? and could a busted power tube completely cut the sound in the amp or is there something else i should be looking for as well (leaking PT)?

also sorry for the long post but could i switch a 5881 for the blown (i dont know) 6V6GT to see if there is any output to the speakers?

and there appears to be no problem with the 6V6GT tube, no discoloration, no obvious problems, a broken key at the pins but am 100% positive, the pins lined up everytime.

[MWJB]

You don't say what voltages you have?

Pull the 6V6 and see what heater voltages you have from pin 2 to pin 7 (use clips & connect up with the amp unplugged from the wall). Then, if you have >6.3VAC, reinstall the tube and measure plate, sceeen & cathode voltages.

If the 6V6 is blow then no, you won't have any sound, there's nothing else to transmit sound from the preamp to the OT. Most blown tubes look fine on visual inspection.

I wouldn't leave a 5881 in there for long, plate current will rise as will cathode voltage (usually beyond the 25v cap that most people fit) and the cathode resistor will be stressed. For a quick test to determine wherther the amp works you should be OK.

[adammerah]

well the thing is i am looking at 6v6 diagrams and i dont see any reason why the tube would blow under those voltages. I really dont know what the voltages are unless i assume that they are what they are coming out of the PT.

It doesnt make sense that the preamp tube would heat up and the power wouldnt unless there is a problem with that tube. i will try out the 5881 and hopefully something comes out of the speakers. now i know the 5881 isnt a permanent solution thanks.

and i just want to make this clear, the amp makes ZERO discernible sounds.

I am a little confused on how you want me to check the voltages. Unplug the 6v6 and plug in the amp and measure the heater voltages from pin 2 or 7 to ground?

[adammerah]

two more things:

MWJB i have read alot of your posts and you are really good at what you do, and definitely know your way around. Respect

and sitting here at work, i just realized that i didnt connect pin 2 AND 7 to 6.3 heater wires, only pin 7, and 2 to ground.

that is one solution but any ideas how that would effect the output (lack of sound)? could i have OT wires crossed for the speaker jack?

[MWJB]

You did admit to putting the tubes in the wrong sockets, and that the 6V6 has no keyway...it would be very easy to blow a tube...imagine if a pin expecting 25vdc at low current suddenly gets hit with 6.3VAC at 2 amps, or vice versa?

OK so you want to measure AC volts from 6V6 pin 7 to ground. I trust that you did not connect the PT centre tap (grn/yellow) if the amp had one? This should be insulated & not connected.

If the OT wires are crossed you would most likely have a howling sound coming from the amp, rather than no sound. Check that the actual speaker plug is making good contact.

Measure DC voltages, to ground (chassis), from pin 8 of the 5Y3, pins 3,4 & 5 of the 6V6 and pins 1, 3, 6 & 8 of the 12AX7. The easiest places to measure these are where the wires from the tubes join components on the circuit board, rather than at the actual tube pins (except for 6V6 pin 3). If you are not used to doing this, use a meter with clips and connect up with the amp powered down & unplugged from the wall. After reading power down, unplug rom the wall and make the next connection, always checking connections are good & no chance of shorts.

[adammerah]

well i broke the keyway when i was pulling the tubes out so it couldnt have been misaligned. -the big screw up was switching them.

now if pin 2 of the 6v6 was grounded and not connected to 6.3v (while 7 is connected to heaters) could this result in the lack of noise i was experiencing? it doesnt seem like it would.

the OT i have is a hammond fender replacement with no center tap. the output wires are yellow and black (com). i believe the yellow is connected to the circuit output and the black is grounded, that doesnt seem problematic.

i am at work so i will definately jump on the amp as soon as i get home.

i have a feeling i am going to need your back up MWJB. but it might all turn out well.

[MWJB]

"the OT i have is a hammond fender replacement with no center tap." It's the PT centre tap NOT the OT I'm concerned with...there should not be one connected with the one wire daisy chain heaters you have.

"now if pin 2 of the 6v6 was grounded and not connected to 6.3v (while 7 is connected to heaters) could this result in the lack of noise i was experiencing? it doesnt seem like it would." No, it wouldn't, this is the way Fender made them.

If you have any pics of the chassis that might be helpful, as well as the voltages.

[adammerah]

MWJB, so I did some digging and it seems more screwed up than before. The yellow 5VAC 2A PT leads to the rectifier were 5VAC across the pins and 1.6at pin8. Red PT leads were 375VAC across the rectifier pins. All heaters were at 6.3 VAC across, the power tube voltages are 1.8V at pin 3 and 4, 5. The bottom rail ()ungrounded ) of the big capacitors (filter caps????) were at 1.8Vat the first 3 nodes and after that I couldnt find any readings.



VDC

please help

[MWJB]

LH vol pot tab is empty, this should be grounded. Middle terminal of pot feeds V1, pin 7, double check. I would strip this wire from out behind the board and replace with shielded wire to V1, pin 7, shielding is grounded at one end only, to vol pot LH lug. Heat shrink the jacket at other end to prevent shorts.

Not related but you have missed off the 25uf/25v cap from V1, pin 3 that bypasses the 1.5K resistor, unless you are a harp player, you probably want this cap (rare to see a 5F1 without one).

Where does the PT centre tap terminate? This is the red/yellow wire, it should go to PT bolt ground.

Black wire from OT appears to be hanging in the air, not connected to speaker jack? You appear to have the hot secondary (yellow) connected to the grounded spkr jack terminal. This wire should go to the hot speaker jack terminal, along with the NFB wire from the 22K (red/red/or) resistor on the board.

You should only have one green wire coming from the PT to pilot (other pilot terminal is grounded), then to V2, pin 7 & V1 pins 4& 5. The second green wire from the PT goes to ground. V2 pin 2 is grounded, V1 pin 9 is grounded...that's if you want to do it the old, noisy way. (I would recommend rewiring as a 2 wire twisted pair, one side goes to 6V6 pin 2 then to 12AX7 pins 4 & 5 - the other wire goes to 6V6 pin 7 and 12A7 pin 9. From each side of the heaters run a 100ohm resistor to ground - wait til you have the amp working before doing this, it just reduces noise).

You should be using switching jacks for input & speaker jack. Run a buss wire from back of vol pot to input jack ground. Run preamp grounds to input jack ground. Run PT centre tap (red/yel), one of the green heater wires, 16uf filter cap ground wire, 8uf screen filter cap (feeds V2 pin 4) all to a bunch of solder tags under a PT bolt. Ground from last filter cap (rightmost) goes to input jack ground.

It's best to have the OT primaries exit near the filter caps and the secondaries exit near the speaker jack, you have these the other way round.

Pull all the tubes and measure resistance to ground at each of the filter cap "+" terminals, you are checking for shorts.

I suspect that you have tried to build this amp from just looking at the Fender layout...unfortunately there is not enough info on any of the Fender layouts to teach you how to build a properly working amp. Check out whatever photos you can get your hands on of successful 5F1 builds & compare.

Tip: you have used white wire everywhere as your hook up, fine if you're sure where everything goes, but many more experience folk than you use one colour for cathodes (6V6 pin 8, 12AX7 pins 3 & 8) another for grid wires (6V6 pin 5, 12AX7 pins 2 & 7) and another for high voltage & plate wires (12AX7 pins 1 & 6). Doesn't really matter what colours you use as long as they make sense to you (e.g. red for plates/HV, black for cathodes, white for grids?). makes visual inspection/fault finding easier too.

[MWJB]

Just another quck thought...that 1.8v you mention was that dc or AC? Voltages at rectifier pin 8, 6V6 pins 3, 4, 8, 12AX7 pins 1, 3, 6 & 8 are all read in dc to ground.

[adammerah]

MWJB,

I did some checking up on the specifics, on the 6V6 the pins are either getting 1VDC or nothing (besides the heaters). I checked for continuity or connections and they all seemed good. and on the 5y3gt the leads are all in and seem to be getting the right voltage (though really hot to the touch, more so than my 4x10 bassman), 375VDC and 5.3V. there is no power gettting to the filter caps either, same voltage at the node as the 6v6 pins, 1V or none at all.

Now knowing that i am thinking about a couple of things,
1. the 5Y3GT tube that i am using a NOS RCA one, could it be bad even though it looks like i am getting good voltages at the pins?
2. the 6V6 could be blown by plugging it into the power tube slot. How could i check?
3. Are one or both of the transformers busted? Is the OT resilient? How would i check?
4. a bad connection somewhere.

can you guys help me narrow down the list. im not sure how or where to start.

thanks,

adam

[MWJB]

Adam,

"5y3gt the leads are all in and seem to be getting the right voltage (though really hot to the touch, more so than my 4x10 bassman), 375VDC and 5.3V." I'll assume that's 375AC to each leg (pin 4 & 6).

I did put some troubleshooting suggestions in my last but one post: 02:16 11/04/08. Which of these have you carried out?

Pull all tubes and measure resistance from filter caps "+" to ground, you are looking for shorts (may be a very short beep if using 'continuity' setting while caps charge up, but beep should not be sustained).

Assuming no shorts, replace rectifier, power up - still no voltage on pin 8, try a new rectifier. Double check that you have continuity (0 ohms) from pin 8 of rectifier socket to "+" of first filter cap (16uf).

How do you check that the 6V6 is OK? Swap it for a known good 6V6, if neither works it's not the tube.

Measure the resistance from the first filter cap (16uf) "+" to pin 3 of the 6V6 and tell us what you get (200-300ohms?)..not the most accurate method of checking an OT but may give some clues. If your OT isn't getting any voltage it is unlikely to be damaged.

Bad connections - several were mentioned in the aforementioned post - re-read this post (02:16 11/04/08). If still no joy, lift the circuit boardand highlight off EVERY eyelet as you check it against a layout.

[adammerah]

Yes. 375 to each leg.

I did check for shorts in the filter caps and i am almost positive that there were none (cause i would have fixed it), i cant verify cause im not at home.

One question you did not answer was if the 5Y3GT rectifier is bad or there are problems associated with NOS. It looks like it was made in the 60s and really that is the direct line of power to the circuit. What sign should i be looking for to know it is bad? is 375 V, or the heaters working good enough to say that its fine?

also i am not sure of the tube type, but would a bassman 5f1a rectifier (5AR4???) tube be able to replace the 5Y3GT to check if it is broken?

i will check that OT.

Thanks

[MWJB]

The easiest way to see if the rectifier is bad is to replace it, put in the GZ34/5AR4 and watch while the voltage climbs at pin 8...when/if you get to 430vdc turn the amp off (we don't yet know what B+ voltage your amp will settle down with so we're being on the safe side and not playing the amp, or subjecting it to overly high voltage.

The 5VAC and 375VAC only tell you that the PT is putting out this voltage, if everything is wired up right and you have no DC at pin 8 then you probably have a bad rectifier.

Many NOS 5Y3 are still functioning OK from when they were fitted to amps 40 or 50 years ago.

Usually a bad rectifier will take the fuse with it.

[adammerah]

Alright here is some evidence.

I checked for continuity from pin 8 (5V 2A) of 5y3gt to the filter caps and there is a solid connection, but the wrong voltage when the amp is turned on. The first node at the filter caps was 1.2V and kept cycling very slowly from 0 to 1.2V over minutes. Pins 2 and 8 were 375V to ground.

On the 6V6 Pin 3 is 1.2 and over time increased to 1.213, pin 4 is 1.19, pin 5 is 3.38 and pin 8 is 0V.

On the 12ax7 pin 1 is 1.18V, pin 2 is .389 (and at input 2 it is .379 while input one is 0 and i had a jack plugged into input 1), pin 3 is .007V, pin 6 is 1.17, and the node between the .02 caps and 100k resistors is 1.19V.

I really have no idea what is going on right now. Voltages are increasing then decreasing, is the 375V lead from the PT supposed to be connected with the filter caps? and if not then how is the filter caps supposed to recieve 340V from a 5V 2a pin?

thanks