Help with 5e5a startup

[CapnCrunch]

Hey all,

I know this isn't a TW or a Dumble clone, but I'm hoping for a little help with start up on an amp that I recently finished. I built a bulb limiter last night, and after a full day of yard work....... I got around to plugging this build in for the first time about an hour ago. I pretty much followed start-up instructions in the Express build guide. This is obviously not an express, and I have some things going on that I don't understand.

I built this amp with a Mojo chassis and board, and Allen Amps PT, OT and choke. I used the Fender layout from the field guide, with alterations ala the layout from Weber and Ceriatone. I was going to add a bias pot but didn't have the parts and decided to build it without and add it later.

I plugged it into the bulb limiter without tubes and checked some voltages. This is what I have.
1. Plug into limiter, check voltage at fuse, it is 120V, hot leg of power switch is 120V. No voltage anywhere else.

2. Switch Power switch on (standby off) Bulb in limiter does not light, Pilot lamp in Amp does not light. Check voltage at hot leg of Standby switch 138V. Check voltage at pin 2 and 8 of Recto 138V. Voltage at pins 4 and 6 of Recto are 317V. Voltage at bottom of 6k8 bias resistor is 40V.

3. Flip Standby on. Bulb on limiter does not light. Pilot Lamp does not light. Voltage at standby switch goes to 0. Voltage at Pin 2 of Recto is now 2V pin 8 shows 0. Pin 5 and 6 of power tubes show -40V. All other pins on power tubes show 0v. Pins 4 and 6 of Recto still show about 317V.

I plugged my 5e3 into the limiter to make sure it works, and it works as described in the Express build guide.

Here is a link to Ceriatone layout I borrowed from. I can't seem to figure out how to attach pics. I keep getting the message "tried to upload empty file". I'll keep trying

www.ceriatone.com/images/layoutPic/fend ... 100508.jpg

Thanks in advance for any assistance

[CapnCrunch]

Update.....

I got impatient and plugged the tubes into the amp and flipped the power switch on. No smoke and the limiter bulb came on and then dimmed slightly. The Pilot lamp did not light at all. I checked a couple of voltages then turned it off. Pin 2 on the Recto had like 18V. The high voltage taps from the PT at pins 4 and 6 on the recto had like 68 volts. No voltage on the heaters at all.

I have a 25 watt bulb in the limiter. I couldn't see that the Recto tube lit up at all. Neither did the power or pre amp tubes which makes sense since there seems to be no power at the heaters.

The PT that I got from Allen amps is his TP40 PT. It is a 340-0-340 with a HV center tap, 50V bias supply, and Center tapped 6.3V and a shield ground. I used a star ground scheme similar to the Ceriatone layout, and I grounded both the HV center tap and the 6.3V center tap with the shield ground on one leg of the star ground. I definitely have continuity to ground on the pins where the HV taps attach to the Recto. and on the heater pins.

The 18V reading on pin 2 of the Recto scares me. It should be close to 5V shouldn't it? I may loose what patience I have and just flip the standby and see what happens. My dad's words keep ringing in my ears "Science and skill, my son, beat brute force and ignorance any day". My patience level seems more compatible with the brute force and ignorance though.

Still can't get my pics to load........

[Allynmey]

Shrink the pics down to less than 2MB each and try to repost. Put a 100w bulb in the limiter. Sound like you have the tranny wired incorrectly or forgot a center tap. Post clear pics should be easy to see the problem.

[CapnCrunch]

Another try with the pics. Still get them to upload. I wonder if there are issues with Iphoto.[/img]

[CapnCrunch]

Another try with the pics.

[CapnCrunch]

Another update:

After struggling to post pics, I thought about this for a while and decided to re-flow the 6.3v CT and the heaters where the pilot lamp attaches. I now have a working pilot lamp. My voltage was still way off on the Recto.

As I said, I used both the Ceriatone and Weber layout (which is exactly the same as the original Fender layout, with the exception of a 6k8 bias resistor vs. 10k). Ceriatone omitted the .047 cap to ground off the standby switch, so I did too. I installed the .047 cap last night, and the voltage on my Recto is now much closer. It now is about 6 volts on pin 2.

I went ahead and plugged it into the wall, plugged in a speaker, and checked some voltages, they seem somewhat high. I didn't write them down, so I'll post them later.

The other issue I have is that the amp makes no sound. Plugged into a speaker and with a guitar plugged in, it is dead. No sound at all, and there is no difference when you flip the standby. I am suspect of how I wired the output jacks. I improvised on them. I will try to post a pic of that, but have been having issues.

[Structo]

On your second speaker jack, is that wired correctly or is the tip shorted to ground?
If that is wired incorrectly it will kill the sound since it will short the signal to ground.
Usually the second or extension jack is not a shorting jack but the first jack frequently is.

[CapnCrunch]

The second (4 ohm) output jack is a shorting type jack. I have a non-shorting jack, which I can swap in. I was just heading back to the garage to write down my voltages which I'll post later. I think I'll just rewire that jack at the same time and see what happens.

Here are a couple of pics of the jacks:

[CapnCrunch]

The second (4 ohm) output jack is a shorting type jack. I have a non-shorting jack, which I can swap in. I was just heading back to the garage to write down my voltages which I'll post later. I think I'll just rewire that jack at the same time and see what happens.

[Sonny ReVerb]

Yes, I think your output jack wiring is not correct. With a shorting jack for the extension speaker, if you don't have an extension speaker plugged in the signal is shorted to ground. You don't have to swap the jack, just disconnect the shorting lug.

Here's a pic of a Fender type setup with a switch for 4/8 ohm.

[img:349:239]http://img101.imageshack.us/img101/7725/outputjacks.jpg[/img]

Are you running one jack at 8 ohm and one at 4 ohm? If not, you shouldn't have both taps connected to the jacks. Normally, I think the Fender jacks are set up with the 8 ohm connection for one 8 ohm speaker or two 16 ohm speakers. The Fenders were pretty tolerant of a mismatch, though. I think a lot of folks got away with two 8 ohm speakers.

[CapnCrunch]

Yep,

The idea is two jacks ,one 8 ohm output, the other 4 ohm output. The OT has a 8 ohm and a 4 ohm tap. I re-wired the output jacks and removed the grounding jack on the second output. I replaced it with a non grounding jack. It made no difference. Still no joy.

Is it kosher to simply tape off the 4 ohm tap and not use it? It is unlikely that I will use it anyway. I have a 50+ year old 8 ohm Jensen P15N that I will run in the combo cab. I made the cabinet the same size as a low power tweed twin so that I could mount a different baffle with 2x12's if I want to. If I do that, I have some 16 ohm green backs that I'll use, so they'll end up at 8 ohms also.

If this would work, I'd like to use the other output jack hole for a bias pot.

[Cliff Schecht]

Nothing wrong with not using the 4 Ohm tap.

Do you have access to an oscilloscope? If you do then you can start testing by installing the tubes systematically, starting at the first preamp tube, and seeing if signal is coming out of each consecutive stage. This is the quickest method I've found for troubleshooting no sound situations and lets you isolate which stage(s) are causing trouble. If it doesn't even work at the first stage then you have trouble somewhere else in the build.

[Structo]

Hmm, so nothing out of the speaker? No hum, nothing?

If you aren't getting anything out of the speaker, make sure the speaker works as well as check the speaker cable.
I had a bum speaker cable one time that lead me on a wild goose chase for about an hour.

If those both check out, check the continuity of the output transformer.

When you probe the plate tubes and grids are you getting any popping noises?
If you don't have a signal generator you can take a low level audio source like a radio or such and inject it at the different stages to see where the problem lies.
I like to start at the PI and work towards V1, be careful with the volume setting on the source as it can get real loud if you probe the wrong thing.

[CapnCrunch]

With the power and standby on, I get nothing...... no hum, no hiss, no thumps, or pops when I touch any of the pins on any of the tubes. I understand continuity, but specifically how do you check continuity on the OT?

I played through the speaker and cable for several hours the other day with a different amp, so I think the speaker and cable are O.K. but I'll double check.

Thanks for the ideas and help. This has me scratching my head. I triple checked all the components, jumpers, and connections. I don't have a signal generator or an O scope. How do you apply a low level signal to the various stages?

The one thing that I haven't done yet is to go through the amp from Power supply to Pre Amp and document my voltages. I will try to do that tonight. Is there any risk to my power tranny if I run the amp long enough to get voltages?

Again, thanks a ton to all of you that have tried to help. I've said this before, but I'll say it again, the Amp Garage is an awesome place.

[Phil_S]

Continuity is OK wihen you get some Ohms on a reading for two ends of the same winding. If there is a center tap, it needs to be lifted from the chassis. If you get an open reading or infinity, there's a problem.

You've already tried the amp and you haven't let any smoke out yet. Go ahead and get the voltage readings. Your lightbult isn't shining bright, that means there are no shorts. Stop using it because you can't get good voltage readings with the bulb in the circuit.