Heyboer JTM100 OT

[rooster]

I just installed this in a Ceriatone factory built JTM100 amp (quad of Gold Lion KT66s). A little history, the amp has a few extras installed in it: a half power switch, a PPIMV, a 3-way NFB switch (different than the Robinette 2-way although it occupied the same type switch), and a non-powered EFX loop. The owner had it for a 6 weeks, played it a total of maybe 10 hours over that time period, and then the output power dropped radically, maybe 75% - but - the amp still had audio. Somewhat strange. Measuring the OT, one primary side was 14 ohms, the other 26 ohms. I said he needed to replace the OT, and that all the other voltages were correct. Also the power tubes were (although not a well matched quad/38-32-28-35), fine. The customer called Nick and he was (so far) helpful offering to replace the OT. Both the PT and the OT were stock Ceriatone trannys (China built?), and, based on the fail, the customer wanted to try something else. FWIW, Nick wanted to see the OT and it is being mailed back to him for examination in the next few days.

For the replacement Heyboer OT build, I suggested that he call Phil at Heyboer. Here I learned that Phil has turned the tranny build process over to a (young?) man named Arlyn. OK., times change. The build took a while (3 weeks) and cost more than I expected (definitely in the MM range if not higher), but It seems a nice sounding OT into a Pure64 1/12 cab loaded with an early version EVM12L. I had played the original Ceriatone when the customer first got it, and now tonight I played it for 20 mins in a large garage, (Brilliant channel @9 o'clock on the volume, T@12 o'clock, M@12 o'clock, B@ 12 o'clock, P@ 12 o'clock, MV @ Full. Using a typical SC Tele, the amp is loud, spanky, and sounds (IMO) great overall. The original play experience with the original OT was good, too, but not remarkable in the JTM100 KT66 way, and yes, I've played one. Anyway, I walked away, let it burn in for 2 1/2 hrs and then turned it off. I'll give it another go tomorrow (with ear plugs).

Some additional info: the 'Half Power' switch doesn't take out a pair of the KT66s as you might think, but instead ties the screens to the plates. Also, something I had never considered before: If you install the typical (JCM800 style) Marshall 1M pot MV, you are rather screwed installing an EFX loop because they occupy the same connection points. Hence the PPIMV used in this Ceriatone amp instead of the JCM800 MV - a MV I actually prefer over the PPIMV in a Marshall circuit. As to the build itself, it looks well done, very neat with wires nicely routed. Sheilded wires are used in all the right places and 1W CF resistors throughout, with 5W wire-wound block ceramic 1K resistors on the screens. The bias pot is 50K lineal and mounted through the chassis near the tubes along with four 1 ohm resistors attached to four digital volt meter connections plus ground point on the rear panel. This model is called the JTM45/100 "Experience" and with shipping to the USA was $1779. The new Heyboer OT was $225 plus $16 shipping.