Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: ginger on March 21, 2018, 05:33:48 pm

Title: Want trem intensity ?
Post by: ginger on March 21, 2018, 05:33:48 pm

I'm recapping this Kalamazoo... STRONG intensity... almost too much , and no intensity knob to tame it .

Title: Re: Want trem intensity ?
Post by: jjasilli on March 21, 2018, 05:57:27 pm

I'm thinking you can replace R13 with a 5K intensity pot, wired like the intensity pot in a VibroChamp schematic.  To avoid using a pot, break R13 down into 2 series resistors adding up to about 4.7K.  They will form a voltage divider.  The trem tube V4a will work the same.  Connect the cathode pin 3 of V1a between the 2 series resistors for less trem voltage.


Whatever you do down around R13 will also alter the gain of V1a.  If you don't like that result, then I suggest you rebuild V1a's cathode circuit to be standalone, and send the trem voltage to that, using the VibroChamp schematic as a general guide.


Hope that helps.

Title: Re: Want trem intensity ?
Post by: shooter on March 21, 2018, 08:37:54 pm

+1

I think rebuilding V1A is your answer, split the cathode R into 2 1.5k to 2.2k, leave un-bypassed. 
I would even go so far is gator-clipping till happy, or go back to original and play surf :laugh:

Title: Re: Want trem intensity ?
Post by: ginger on March 22, 2018, 11:35:20 am

Thanks... how would I slow the speed on this one ? I've done it on many Fenders , but this one already has .02 , .02 , and .033 in the trem circuit .

Title: Re: Want trem intensity ?
Post by: sluckey on March 22, 2018, 11:44:33 am

Change C7 and/or C8 to .033µF. Look at this schematic to see one way to add an intensity control...

http://el34world.com/charts/Schematics/files/marshall/marshall_18watt_schem.pdf

Title: Re: Want trem intensity ?
Post by: ginger on March 22, 2018, 04:24:11 pm

Thanks again... this isn't a build , so I don't think I'll be adding a pot.... I'll change one of the caps  to slow it down a bit though .

Title: Re: Want trem intensity ?
Post by: ginger on March 22, 2018, 04:38:16 pm

I already changed the V1 cathode arrangement from 4.7 K / no bypass cap , to the Fender 1.5K/ 25uf , because of the usual lackluster gain / dynamics of old Gibsonish amps .Also , the Kalamazoo had no cathode bypass cap across the 150K on the output tube....added another 25@ 50uf there also ..sounds nice and full now .

Title: Re: Want trem intensity ?
Post by: jjasilli on March 22, 2018, 05:33:20 pm

 :thumbsup:

Title: Re: Want trem intensity ?
Post by: 2deaf on March 22, 2018, 11:40:55 pm

What if you lower the voltage on the node that is powering the vibrato tube?  Like maybe tee-off with a 220K resistor then another decoupling cap to ground and take the 150K plate resistor from that point.

Title: Re: Want trem intensity ?
Post by: 2deaf on March 23, 2018, 11:57:03 am

I believe the attached is what jjasilli suggested in Reply #1, if you ever want to add a knob.

Title: Re: Want trem intensity ?
Post by: ginger on April 08, 2018, 01:40:52 pm

Hi guys... I really like the changes I made to make the amp not be so subdued in tone.. which was just to replace the lone 4.7 / no cap , with a 1.5K / 25uf cap on V1 , and put a bypass cap across the EL84  cathode resistor . When I hit hard notes , there is a pumping sound .. as if the trem is treming for a few seconds . do you see any reason why that would happen with the only two changes I made . The trem is on a switched pot... maybe still bleeds signal when switched off ? I would leave it alone.. but is really distracting

Title: Re: Want trem intensity ?
Post by: ginger on April 08, 2018, 01:44:40 pm

I didn't notice it before I put the chassis back in the cab... then , after my girlfriend left , when I could turn it up... I noticed the slight trem

Title: Re: Want trem intensity ?
Post by: ginger on April 08, 2018, 01:50:45 pm

maybe what I did on V1.... just the usual Fender 1.5K / 25uf  , almost compressing way too much for a couple of seconds

Title: Re: Want trem intensity ?
Post by: sluckey on April 08, 2018, 02:55:08 pm

When the trem switch is off, the trem effect should be dead. I think you are hearing something else. Maybe caused by your mods. Remove them one at a time to see if they are the cause.