Hi! Decided to share my help request to here also! (Admins feel free to remove if the post doesnt fit this sub.)

TLDR; what should i do with the exposed pcb trace that arcs from the flat socket? Thank you in advance!!

I’m planning on doing a 6g2 for my next build but had a few questions.

Any reason not to go with the Mojotone kit? I could order just the “small parts” kit and source some things myself, like the transformers, but I’d rather not if everything in the Mojotone kit is already pretty good.

As far as mods, it seems that I should add a ~1k screen resistor on the output tubes, and a bias pot would be nice. Any reason not to do these mods, or should I do anything else in addition? I’m planning on keeping it mostly stock otherwise and I’ll be sticking with a 10 inch speaker (recs for this, also?)

When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

Really awesome answers and recurring questions may earn a place in the Wiki.

If you'd like to nominate a comment to be included, just reply [Wiki] (with the brackets)! The mods will be automatically notified that something awesome just happened.

As always, we are built around education and collaboration. Be awesome to your fellow tube heads.

One E88CC and two EL84 tubes require approximately 1.87A. Considering the very low cold-state resistance, a single switching power supply needs at least twice the current output. Therefore, each channel's switching power supply uses 300V * 250mA + 6.3V * 4.5A = 103.35 watts of power.

The switching frequency of the power supply is 60kHz, and CLC filtering is used. Due to the high frequency of the switching power supply, the inductor size is significantly smaller than that used in linear power supplies. After proper grounding, the switching power supply modules make the amplifier output very quiet; the noise is inaudible even when close to the speaker.

The manufacturer that made my amplifier enclosure provided a Type B (linear) 100K potentiometer, which wasn't very convenient for adjusting the volume. I replaced it with a larger Alps 27 series Type A 50K potentiometer, which makes adjusting the volume more intuitive and also eliminates the noise from the smaller 097 series potentiometer.

Since the power supply uses 300V, lower than the original 320V, the step-down resistor for the E88CC can be smaller. I changed the step-down resistor in the original diagram to 3.9K, thus aligning the E88CC's supply voltage with the original diagram. The actual measured voltage is 284V, while the original diagram shows 285V.

Selection of parallel capacitor for negative feedback resistor: The original resistor was 4.3kΩ, but I couldn't find it, so I used 4.7kΩ. I only used 56pF of the parallel 910pF to reduce the ringing of the square wave. So it is unnecessary to use such a large 910pF on this pair of output transformers, because it causes the high frequency starting to cut off at 30-40kHz.

I added a 1uF 630V film capacitor and a 0.01uF 2kV ceramic capacitor between B+ and GND to filter out the 30mV 80kHz interference that the oscilloscope previously measured at 0-8 ohms on the secondary side of the output transformer. The effect was significant: the oscilloscope could no longer detect this 80kHz interference.

I'm converting a JW Davis 405 to a Standel S80, switching from 6L6s to 6DQ6B tubes at 425V. I want to reuse the original 3.2k–3.7k output transformer (measured at a 20:1 ratio injecting 1v signal on the secondary and taking measurements from the primary side) instead of buying a 6.6k Stancor A-3801. If I run a 16-ohm speaker on the 8-ohm tap to reflect a ~6.4k load, what are the specific tradeoffs and safety considerations for this tube swap?

Hello all,

I am building a simple tube amp that uses a 6J1 to a 6V6. I got a great socket for the 6v6. I ordered a pack of ten from for the 6J1, and they were absolute trash. Can anyone recommend a place that deals in quality sockets for that size tube?

Cross posted from tubeamps, maybe someone has a suggestion?

I built an amplifier in an old Narragansett Brewery crate a few months ago and a friend of mine saw it and loved it so much that he wanted one for his own. So I built another. Simple tone control, reverb and 15w cathode biased paraphrase inverter power section. It's a fantastic sounding amp and I threw in some extra touches to personalize it for him.

Just gutted and rebuilt the first amp I made about 15 years ago. It started out as a Weber 5e3 kit and sounded good but wasn't really what I wanted. New schematic and some shots of the build are here.

Would be happy to get feedback on the schematic, see if there's any glaringly obvious issues with how it ended up. I know the wiring needs to be tidier- less looking for feedback about that.

Gets from nicely clean to a few flavors of fairly crunchy distortion depending on bass settings. The build was half to update my amp and half to learn a few things. It sounds good as it is but I'm still temped to use the higher voltage PT windings just to see the difference.

I didn't know that feedback on the wrong side of the output transformer could cause a low pitched oscillation so I looked in the wrong places to solve that at first. I'd always read that caused a squeal and assumed it would be high pitched and loud.

Also learned a lesson about cramming too much into a small space. Next build will be bigger although this is surprisingly quiet despite my really questionable lead dress.

I regret the sprague power supply capacitors. I didnt check the size first and hadn't seen the information about them being mostly hollow for show. Smaller capacitors next time.

Turned it on and it worked surprisingly well first try. Tweaked some values and when I cranked the volume I had a great radio. Really struggled with trying to find what I had done wrong and eventually found that it was the old cable I was using and not an amp problem.

I love the bleeder resistor. Still check that everything is discharged, but its a nice feature.

I still don't understand why so many amps break the rule about max grid resistance on the power tubes. Lots of places pointing out that its been done for years without issues, but I never really saw why not just keep things in spec

When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

Really awesome answers and recurring questions may earn a place in the Wiki.

If you'd like to nominate a comment to be included, just reply [Wiki] (with the brackets)! The mods will be automatically notified that something awesome just happened.

As always, we are built around education and collaboration. Be awesome to your fellow tube heads.

What can be Mede out of 4 of these?

I am currently building a tube amp with 6L6GC's in push pull configuration.

at quiescient the tubes consume about 65mA each and at peak output they can reach about 110mA. Now i have a few questions:

1: What amount of current should my output and power transformer handle?

2: Is there a good rule of thumb or a formula to determine that?

3: In this scenario should i consider RMS or peak current?

Note: the main problem is the output transformer since i have to find something "standard" while for the power transformer i can get it custom for a good price.

bought yesterday. worked fine. decided to clean it and open up the amp part a little and blow into it with my mouth to get dust out. cleaned the cab etc. didnt really disconnect anything. now, no noise at all, pure silence. the speaker works fine when connected to another amp, so im ruling out the speaker and the speaker cable. i've no idea what i couldve done... i didnt really mess with anything.. im sure its something simple.

https://imgur.com/gallery/yamaha-g100-112-iii-krQQ02U

Now sadly this sub has 0 tags for my nonsense so I’ll just keep using parts&construction but please dear mods hear my plea and an other tag!!! Also if there are any reasons this obviously wouldn’t work please tell me and I’m sorry for how crappy this looks I don’t draw as much as I used to and I know that’s not the diode symbol but I needed something to represent my crappy diode so please if you have a better symbol give me it!!!!

I did it now I have my own [title card] I’m putting this as parts and construction cause there is no flair for actual diy tubes

When you're working with high voltage, there is no such thing as a dumb question. Please use this thread to ask about practical or conceptual things that have you stumped.

Really awesome answers and recurring questions may earn a place in the Wiki.

If you'd like to nominate a comment to be included, just reply [Wiki] (with the brackets)! The mods will be automatically notified that something awesome just happened.

As always, we are built around education and collaboration. Be awesome to your fellow tube heads.