TRIWATT "PAGE MODE" SWITCH

[ViperDoc]

I just got invited to join a year-long prep for a Pink Floyd cover band and was asked if I had a Hiwatt. I said "YES, but it won't be ready for a couple months..."

I have a Trinity Triwatt kit that I'm going to build. I was looking at the SCH and noticed two preamp cathode bypass arrangements that were found in Jimmy Page's DR103 (see the Tweaker table notes in the LL corner of the Triwatt SCH below). I thought I could place these on either a DPDT switch or relay (or two SPDT relays) and have a "Page Mode" control that switches those in.

My question is: Are there SPDT relays you know of that are small enough to mount on a turret board? The amp has a 5V power supply and relay for the Overdrive circuit, I could use that for the Page Mode power if I wanted. I thought it might be best to place the relays on the ground side of the circuit, is that right? Please see the attached drawing.


12-11-2-21 CORRECTED SCH :

TRIWATT PAGE MODE.pdf

Here are the default SCH and Layouts:

TriwattSchematic.pdf

TriwattLayout.pdf

Thanks.

[Colossal]

I would think carefully about trying to place a relay on that already-packed turretboard. You are asking for coupling the noise from the relay coil. Also, as drawn, those mod switches will pop. The mod switch should have 100k-1M to ground to always allow a path for the cap charging current to trickle.

EDIT: thinking about this a little, you probably could post a little daughter board up on standoffs, and let it sit well out of the way and above any nearby components

[ViperDoc]

I would think carefully about trying to place a relay on that already-packed turretboard. You are asking for coupling the noise from the relay coil. Also, as drawn, those mod switches will pop. The mod switch should have 100k-1M to ground to always allow a path for the cap charging current to trickle.

EDIT: thinking about this a little, you probably could post a little daughter board up on standoffs, and let it sit well out of the way and above any nearby components

Good idea. Since the OD relay sits on the back wall of the chassis and connects to two pins on the V2 socket, I could place the other relays on either side and intercept the cathode wires on V1 and V3 with individual SPDT relays to minimize the wire runs.

I found this as a possible option: https://www.pololu.com/product/2480

Regarding the 100K-1M to ground on the switch, how does it trickle when the switch is open? Would you put it across the switch? How would you handle the SPDT on V2? Thanks!

[Colossal]

Regarding the 100K-1M to ground on the switch, how does it trickle when the switch is open? Would you put it across the switch? How would you handle the SPDT on V2? Thanks!

Yes, across the switch. You want Rpop to be such that it and the stuff in series with it above (your 2k2/100n boost) appears to be very large to R6, when it is out of the circuit (boost switched out).

[xtian]

I just got invited to join a year-long prep for a Pink Floyd cover band

OMG. I dream about this happening all the time. I hope there's lasers!

[ViperDoc]

I just got invited to join a year-long prep for a Pink Floyd cover band

OMG. I dream about this happening all the time. I hope there's lasers!

I might cue them to all of my wrong notes so people get distracted.

[pompeiisneaks]

I just got invited to join a year-long prep for a Pink Floyd cover band

OMG. I dream about this happening all the time. I hope there's lasers!

That reminds me of when I was in my early twenties and went to the local planetarium for a Pink Floyd laser show, what a blast!

~Phil

[mhuss]

+1 on a high value resistor across the relays to avoid popping

Also consider SSRs, no coils to worry about. Molten Voltage and others make ready-to use modules.

I remember laser shows at the Fels Planetarium at Franklin Institute in Philly.

[ViperDoc]

Much appreciated, all. I’m going to put it on a switch for now. It doesn’t seem like the thing I’d need or want to kick on/off while playing. I’m building the board right now…

[ViperDoc]

I just noticed I errantly put a 100 nF cap on the V1 mod instead of the 100 uF that's in the Trinity SCH. CORRECTED. Carry on.

[ViperDoc]

I fired this amp up today. I even made sure my bias voltage was in the neighborhood before putting in my power tubes! Hey, it only took me about 4 builds.

The Page mode switch is noisy with 1M resistors across both switch poles, but it’s not the type of thing I’d switch while playing. The Page values really tighten up the headroom when playing cleans as well as changes the feel of the overdrive. I only had a 100V cap on hand, and I'm going to replace it with a 25V version. It’s a really nice option for this amp, which has a very unique clean to overdrive palette, it’s unlike any other amp I’ve played. I’ve been running a Tyler Classic through it into an Avatar Forte 212 with Fanes. Glorious!

The schematic shows other such mod values for Townsend and others. This a wonderful kit build for Hiwatt tones. Steve has been more than helpful with my questions. Highly recommended.

[ViperDoc]

MERRY CHRISTMAS ALL!

Hey, I was looking at my voltages compared to the schematic on this build, the PI plate voltages listed for this DC-coupled LTP are 274 VDC and 236 VDC for each plate. My plate voltages are 278 VDC and 284 VDC. My other voltages are in the ball park, so I will simply increase the second triode's plate resistor value to knock that down.

My question is, what does such a large PI plate voltage difference aim for in the Hiwatt-style amp? I've never built one of these, I'm used to Marshall-style LTPs with 2x100K or the 82K/100K plate load design. I'm just not used to seeing such a disparity in the plate voltages.

Thanks.

[martin manning]

Hey, I was looking at my voltages compared to the schematic on this build, the PI plate voltages listed for this DC-coupled LTP are 274 VDC and 236 VDC for each plate. My plate voltages are 278 VDC and 284 VDC. My other voltages are in the ball park, so I will simply increase the second triode's plate resistor value to knock that down.

If the triodes in the 12AT7 were perfectly matched the plate voltages would be within a volt. I can only conclude that a) the triodes in the tube used to get the voltage readings in the Trinity schematic were very poorly matched, or b) one of values on the schematic is in error. Your voltages look much more reasonable, so I'd leave it as it is.

[ViperDoc]

Very good, thank you, Martin!