{"id":11062,"date":"2022-12-28T12:16:02","date_gmt":"2022-12-28T12:16:02","guid":{"rendered":"https:\/\/www.bartola.co.uk\/valves\/?p=11062"},"modified":"2022-12-28T12:16:02","modified_gmt":"2022-12-28T12:16:02","slug":"gassy-nightmare","status":"publish","type":"post","link":"https:\/\/www.bartola.co.uk\/valves\/2022\/12\/28\/gassy-nightmare\/","title":{"rendered":"Gassy nightmare"},"content":{"rendered":"\n

Ok, title isn’t very appealing. I know, however it truly reflects what I experienced over the past few days. Let me clarify before I start: a gassy tube developed a nice fault-finding journey. You always learn a lot from all this, for sure. Luckily, due to the holiday season, I had the time to work on this. I’d rather have spent it otherwise, but my 300B amplifier was dead. <\/p>\n\n\n\n

\"\"<\/a>
6BY5-GA damper<\/figcaption><\/figure>\n\n\n\n

I had a gassy 6BY5-GA <\/a>damper rectifier tube. I should have changed it, but I was lazy and I paid the price for it. When turned on the 300B HT power supply, it will flash blue for a sec or two and the gas ionisation will disappear after a minute or two when tube was warm enough and operated as expected. Problem was that my stash of these damper tubes was up in the storage, who knows where. <\/p>\n\n\n\n\n\n\n\n

On Boxing Day, I was about to enjoy a lovely morning of jazz records (Thelonious Monk was first on the list) with my coffee when the tube failed miserably when I turned the HT on. A quick flash and could notice that a fuse on the Mains HT delay \/ surge circuit went pop as well. Well, time for a new tube I thought and went up to find them. After some Tetris game with my boxes I found a big box full of them. Grabbed a few and came down to hopefully resume the normal morning with my coffee. But it wasn’t the case. When I tried to fire the amp up, again the fuse went pop. Hmm, it was more complicated than I firstly thought. <\/p>\n\n\n\n

Debugging <\/h2>\n\n\n\n

I took the PS to my workshop and connected a dummy load. I gradually brought the Mains up with the VARIAC and noticed that the mains current was quickly coming over 1A at which point I stopped. Removed the HT filtering PCB<\/a>, and started checking for faults. Not easy as it’s a PCB and components can’t be easily taken out. That’s the price you pay when you’re not soldering point to point. I found one of the UF4007 rectifiers dead – in short. Worst failure. I then replaced them with a pair of SiC 1.2kV\/2A diodes. I suspect that some short developed (not common in tubes) and fried the diode. Perhaps some rectifier tube expert can chip in here to elaborate more. <\/p>\n\n\n\n

Replacing the diodes wasn’t enough. When loaded the PS will only deliver way below the output voltage expected. I wired it to maximum levels and again, 330V maximum with a 600V input. Something was wrong:<\/p>\n\n\n\n

I suspected some damage on the TX secondary windings due to the short created by the UF4007. I then measured the secondary voltages finding to my relief that they were ok:<\/p>\n\n\n\n

\"\"<\/a>
A debugging experience<\/figcaption><\/figure>\n\n\n\n

The problem was on the rectifier. I could see the filaments running well, but something else was going on. I replaced the board with a spare PCB with a full-wave rectifier formed by 4 SiC diodes. The power supply worked well! <\/p>\n\n\n\n

When I removed the Octal socket, I found to my relief that a single core cable connecting one of the cathode was broken. Short peak current damage perhaps?<\/p>\n\n\n\n

I proceeded to replace the socket entirely, it’s a NOS ceramic Russian one. Have a few of these good sockets. As I didn’t trust any of the connections, I rewired the socket again using the new one. The power supply then worked back again as expected delivering 390V at full load (estimated to be close to 200mA). <\/p>\n\n\n\n

\"\"<\/a>
Revised power supply<\/figcaption><\/figure>\n\n\n\n

<\/p>\n\n\n\n

I can now go and enjoy the coffee and the lovely sound of this amplifier. I guess I learnt the lesson.<\/p>\n","protected":false},"excerpt":{"rendered":"

Ok, title isn’t very appealing. I know, however it truly reflects what I experienced over the past few days. Let me clarify before I start: a gassy tube developed a nice fault-finding journey. You always learn a lot from all this, for sure. Luckily, due to the holiday season, I had the time to work … Continue reading “Gassy nightmare”<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_publicize_message":"","jetpack_publicize_feature_enabled":true,"jetpack_social_post_already_shared":true,"jetpack_social_options":{"image_generator_settings":{"template":"highway","default_image_id":0,"font":"","enabled":false},"version":2},"jetpack_post_was_ever_published":false},"categories":[673,158,5],"tags":[610,675,836,971,679],"class_list":["post-11062","post","type-post","status-publish","format-standard","hentry","category-300b-amp","category-se-designs","category-valves","tag-300b","tag-300b-amp","tag-300b-amplifier","tag-6by5g","tag-damper-tube"],"jetpack_publicize_connections":[],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack_shortlink":"https:\/\/wp.me\/p2r2tK-2Sq","jetpack_likes_enabled":true,"jetpack-related-posts":[],"_links":{"self":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/11062","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/comments?post=11062"}],"version-history":[{"count":3,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/11062\/revisions"}],"predecessor-version":[{"id":11070,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/posts\/11062\/revisions\/11070"}],"wp:attachment":[{"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/media?parent=11062"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/categories?post=11062"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.bartola.co.uk\/valves\/wp-json\/wp\/v2\/tags?post=11062"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}