IIb build prep question

[Mehfuzhoss]

Hello el34world,

I am thinking about a iib that will have approximately 30 watts of power, solid state rectifier, with a VVR to control the B+. Will ac30 transformer set will do the job? I want the amp to be smooth and have a 1K sag potentiometer. is this okay to have a 1k pot instead of traditional 200/300 ohms resistor there?

Does using a VVR makes the power transformer hotter or I only have to keep the VVR unit cool by proper heat sinking, I am thinking thermal paste and firmly affix it to bare aluminum chassis.

Since I will not use the ez81, what kind of SS rectifier form should be appropriate? I don't want the amp to be spikey or stiff; i want it to be smooth and slightly spongy and dynamic.

I already have the iib layout, a vvr drawing. I want it simple, VVR control, Tone/Cut control, Master volume.

please let me know your opinion.

Thank you

[Bieworm]

That's a confusing amp build. You want a higher wattage 18 watt, which is by the way already a plenty loud amp. Then you want a VVR to tame that thing?
Why not build a 36 watt? There are plenty examples for that.
And VVR territory is slippery.  You need the right mosfet for that. The rest is simple enough.
And an EZ81 is not saggy as rectifier. I always put a full bridge SS one with a 100R 25W resistor in series. Adds some sag, but firm enough

[Mehfuzhoss]

I put a 220 ohms 5 watt in Superlite TMB that has a solid rectifier as well. it added a very slight sag compared to 150 ohms that it had before. I honestly do not like the idea of vvr and for some reason i have this thought that the power transformer might get strained !!!

I might build a stock iib with ez81 at some later time.

thanks

[Mehfuzhoss]

recently i really liked the spitfire OD. so I changed my superlite tmb mixing resistors to to 220k, before they were 470k. I also changed the input resistor to 33k from 10k. and like i said the sag resistor upped to 220 ohms. it made the amp little bit barkier but I want more bark out of it. do you recommend any other changes that might make the amp more bassier with growl like mid heavy OD??? it has 1750PA OT.

thanks

[Bieworm]

Pretty strange ... I recently built a SL TMB 18W for a customer. I found it really bass heavy, so I added the low cut switch. A switch between .47uf and 2.67uf cathode bypass cap on V1a. And simultaneously the coupling cap between V1a and V1b switch from .0047uf to .022uf.

[pdf64]

… a iib …
… 1k pot instead of traditional 200/300 ohms resistor …

I’ve no idea what you are referring to 
The Mesa Boogie Mk IIb is the only model comes comes to mind, but that doesn’t seem to align with the few details that have been revealed. 
Further detail regarding the amp and the proposed schematic seems a fundamental requirement here.

[Bieworm]

The 18w lite2b
Usually only the normal channel of the 1974,but with the tremolo channel's tone control values

[tubenit]

I’ve no idea what you are referring to  The Mesa Boogie Mk IIb is the only model comes comes to mind, but that doesn’t seem to align with the few details that have been revealed. Further detail regarding the amp and the proposed schematic seems a fundamental requirement here.

I had the same confusion and thoughts!


Schematics sure help out in answering questions.

[PRR]

...or not IIb?

[sluckey]

...or not IIb?

I get it!   

I automatically assumed 18Watt Lite IIB just because I have built one. However, the polite thing to do would have been to clearly state what amp is being discussed and also provide a schematic since this is not a widely known amp. Here's the schematic for those that want to know...