More 5F1 Champ Build problems...this one is strange

[Lightning13]

The 6V6 is damaged goods. Missing alignment pin. I was installing it like a smaller preamp tube. Who knows which pin was ending up where. I've ordered a new tube that should be here Tuesday so hopefully that will get me up and running.

The box the tube came in didn't have any plastic pieces in it and nothing is in the tube socket. Guess I'm just lucky.

I've got a matched set of 6V6's in another amp that I tried earlier but I think I'll keep them nice and safe.

[Bruce / Mission Amps]

"440K on lug 8... that's wrong, it should be 250 to 270 ohms" It's a 5F1 (~470ohms)...you're thinking 5E3....easily done, I did the same when describing Lightning13's cathode wiring for V1!;-)

Oops. No voltmeter should be drawing an arc with respect to ground unless is it actually set for amperage.... so with that and after seeing the power tube and general lack of hands on experience, I'll just stay out of this conversation any further.

[MWJB]

Hi Bruce, yes, it's a little scary!

Lightning13 - I strongly suggest that you purchase some meter leads that terminate in wire grabbers, power down & unplug the amp from the wall, make your connections with the meter leads clipped in place, power up & take a reading.

Power down, unplug from the wall & repeat for the next voltage reading...continually checking that you have the right connections & no chance of shorts to otherpins/components/ground.

If you have a cheapy meter that won't take more expensive clip/wire grabber leads, then by a couple of small, insulated corocodile clips and replace the stock probes on the leads you already have.

This might seem laborious, but it is the safest way, until you are more familiar with what you are doing.

[Chuck H]

Something is perilously wrong. Perhaps it's only the incorrect tube installation. We can hope. But building an amp when you don't even know how to set a meter, how to convey the tested results or even what part of the circuit your testing (ie: nothing fancy, just "first preamp stage", "power tube cathode", etc) can be very dangerous. I know we all start as noobs but to build an entire amp with a new meter, soldering iron and no former experience... Well, let's just say there's bound to be complications.

I would say shelf the project long enough to learn some basics about tube amplifier electronics. Nothing really hairy or time consuming, just things like "first gain stage", second, etc., the basics of how a capacitor or resistor works and how their values are indicated, ohms law and the relationship between voltage and current, the difference between AC and DC and basic tube function so one might understand the relevance of earth/ground in the circuit. With just this knowledge anyone can come to this forum with at least the ability to convey information and understand the advice given to them. Without these basics the whole thing is just folly.

If the interest is in a better understanding of how things work and perhaps the ability to make some basic modifications later, then learning the above before hand (or at least during the process) isn't a tall order and building an amp or two is a great way to learn and benefit at the same time. If saving money by building your own amp is the ONLY goal and you don't really have any interest in putting in the time to learn the basics, your really better off both financially and in quality just buying an amp.

[MWJB]

"Something is perilously wrong. Perhaps it's only the incorrect tube installation. We can hope." In the pics supplied the power tube is installed with the spigot/keyway visible in the socket.

"If saving money by building your own amp is the ONLY goal and you don't really have any interest in putting in the time to learn the basics, your really better off both financially and in quality just buying an amp." Couldn't agree more Chuck, in fact if you are building your own amp purely to save money, it's probably several builds down the line from your first build before you start to properly suss out layout & grounding!

It is possible to build an amp such as this with just some common sense, but you really need to check out some good quality pics of successful builds first & copy them EXACTLY. Onlineshop Startseite have a stage by stage photofile of a 5F1 build at their website.

[Lightning13]

Thanks to MWJB, Bruce, Chuck, and the rest of the gang that helped straighten me out on this amp. It works great and with low noise!

I've included a couple of pics to show how improved the wiring is. I grounded high power items away from the preamp side and I've already taken out the feedback loop to add a little grunt.

Problems stemmed from a broken 6v6 alignment pin (I'm guessing probably broke it when I first tried to install that tube.) This threw off where the different voltages were coming and going from a tube that was simply improperly installed. The tube itself is probably fine. This set off a chain of events: Troubleshooting, wire cutting, rewiring, redoing, and generally digging a bigger hole for myself. So, I ordered in some new wire, a couple new capacitors, and a new tube. The key was to take a step back and look at the project with fresh eyes.

I tinted some lacquer and sprayed the tweed cabinet. Then, I good going over with some 0000 steel wool. It looks like a well taken care of old amp that will be around for a long time. But, it needs company.

Have I obtained amp build redemption?

[MWJB]

"Have I obtained amp build redemption?" If it plays nicely, doesn't hum too much....then yes. Looks better. I'd prefer to see the heater wires from the pilot come straight down to the 6V6 pins, so that they weren't lying on the blue plate wire...but if it's not causing any issues then don't sweat it.

[JoeK]

Someone else had a similar problem (cathode bypass failure) recently. His problem turned out to be DC getting through the tonestack caps and getting to the grid of the power tube in a single end build.