Crate V5 mods... anyone?

[Tele-Dave]

When in triode mode, how dark does it get? It isnt too bad, is it? Darker than amp was before tone mods? It is liveable, isn't it?
Going to do Pent/Tri mod anyway. When you come up with a fix, let me know.

Have to dig thru parts box for cap for Plate/Grid. Will try it if I can find one.
Poly cap? Correct?


Was better price for pots and knobs than I thought it would be. Shipping $6

Forgot to ask for schem for 508. Will call them back in few minutes.

As per R23, circuit looks like 1/2 watt or larger would be o.k., Correct?

Question, I want to put a standby switch in also. Would it be that all I would have to do is to install switch to break power at J1 and J2? Correct?


Thanx Jim----------------Dave

[jim p]

Because of the 1 H choke in the power supply you cannot just put a switch in the HV power supply and expect it to last. In a mechanical analogy a choke is like a flywheel it wants to maintain a constant rate it resists change at start up (building magnetic field) and if interrupted (clasping magnetic field). A choke is what is used to generate a spark on a spark plug in a gas engine. If you put the switch at pin 2 J6 (C15 side) when you open the switch the voltage on the choke will go positive to the point of arcing across the contacts in the switch and at some point the switch will fail. If you put the switch on the other side of L1 (J1 pin1) when you open the switch the voltage on the inductor will go negative but this side will work if you put a reverse biased rectifier diode to ground that can handle a minimum of 150mA and reverse voltage of 400 volts (1N4007 should work). Better is to put diode with a low value resistor in series (50 ohms 1 w) in parallel with the choke (cathode on pin 1 side) it will be forward biased when the choke goes negative with the switch opening. Also consider a bleeder resistor on the C15 side for safety.
Me I don’t believe in standby switches so much I don’t think cathode striping happens at these voltages and currents plus the amp is quiet.
If R23 is the one in parallel with the choke on the PCB 1 to 2 k 1 watt is fine.
For the plate to grid cap minimum 300 volt rating mica or poly is fine.

[Tele-Dave]

[QUOTE=jim p]If you put the switch at pin 2 J6 (C15 side) ------If you put the switch on the other side of L1 (J1 pin1) when you open the switch the voltage on the inductor will go negative
QUOTE]

Was talking about putting switch in leads from power trans to where it connects to J1 and J2 on edge of PCB. Just inserting a DPDT to break legs going to PCB and that way I will also have power to supply Indicator light when in standby. Just going to drop out 240V going to Plates
Shouldn't that be just like turning off main power switch as far as choke is concerned?
Was going to interupt both legs of power prior to going to PCB. Connectors are marked J1 and J2 on PCB, and on schematic it is prior to diode bridge and C14/R24 filter and with R24 at ground, should prevent problems that you describe with choke. Is that right or am I missing something????

[jim p]

Putting the switch on the AC side should be ok and avoids dealing with the choke.

[Tele-Dave]

Putting the switch on the AC side should be ok and avoids dealing with the choke.

That was my concern, and why I thought of puting it there. On some other amp schematics I was checking for switch placement, most of them placed switch on transformer secondary leads prior to any other electronics and if there was a choke farther downstream, and i noticed on some schematics that did not have chokes that they put the switch anywhere downstream prior to feeding plates.
Know about collapsing field in coils, that is why didnt want to break either side of coil, and thought that with R24 biased to ground, would bleed off pulse when field collapses. Should be just like turning off main power switch as far as coil is concerned, or that is what I thought.

Thnx Jim, just wanted to verify. Don't know too much about electronics, but was trained in automotive mechanics when there was Points, Plugs and condensers, (and coils) And understand about a collapsing field in a coil of wire producing high voltage surge.

Called Loud Tech again today 3 times, but message says "Our personel are in Training presently, please call back later." I will keep trying to get thru, would like to have copy of schem just so I can compare to V5.