Traynor YBA1 Bass Master --> Key Master

Jay

Jay

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Happy 2026 gang! I modified a Bass Master over the holidays. I'm calling it a Key Master mod.

At the outset, I decided that I'd try to keep it looking vintage, including the stock push-on knobs. When replacing pots, I turned to Bourns low-friction guitar pots that would accept push-on knobs (PDB241-GTR01 series), since they had a similar feel as the originals. In hindsight, I wish I switched to set-screw barrel knobs so use other pots (with more values), since I couldn't find a mid-pot with the same, low-friction feel.

Front panel: The 'standard' inputs were changed from open-frame to Cliff jacks for wiring purposes. The bright inputs were replaced with switches. I removed the gain label after this photo was taken. I'll label the switches after everything is finalized.

Rear panel: I added a fused IEC receptacle and removed the stock power cable. The circuit breaker was removed and replaced with a switched pot.

Spot any other changes?

I may or may not post this amp in the classifieds section, but it will be available soon. Reach out if interested....

YBA1 with V2 key master mod - front 1.jpg


YBA1 with V2 key master mod - rear 2.jpg
 
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Four additions seen in this photo:
1. IEC for power input on rear panel (top)
2. switched pot on rear panel for depth (pot) and NFB (more/less switch)
3. 12Vdc power supply mounted on a simple white PCB that I designed
4. Filter-cap PCB, which supplies power tube anodes and screens. 10k dropping resistor on board as well

Also, original rectifier diodes on eyelet board replacedYBA1 with V2 key master mod - gut shot - power supply.png with ultra-fast diodes.
 
More on the power side of the amp:
- reworked the fixed bias supply to add a bias-adjust trim pot
- another filter cap PCB for the PI
- replace the 100n coupling caps in power amp with 47n
- rebuilt PI with typical component values in "long-tail-pair"
- tone-stack components moved to front panel pots for low noise
- new 1k screen resistors
- new 100R/100R visual centre tap for AC heater supply
- ground switch disconnected
- twisted-pair wires to depth pot and NFB switch


YBA1 with V2 key master mod - gut shot - power amp.jpg
 
Here is the preamp side of the chassis.
- added tube socket is on far left (top)
- 12Vdc used for filaments of the new tube (V0). Wires are still twisted so they don't pick up AC from the 120V input
- added eyelet board holds components for first gain stage and subsequent inter-stage components
- high input goes to V0a; low input goes to V0b (skipping one gain stage). Cliff Jacks are wired to make this happen.
- the stock 'standard volume' pot is now a preamp gain pot that is situated after the second gain stage
- switch to the right of the gain pot is a 3-position bright switch. Other switch currently wired to fine-tune the high end
- the bright volume pot is now the master volume.
- In all, there are 4 preamp gain stages when plugged into high input (3 when plugged into low input).

YBA1 with V2 key master mod - gut shot - preamp.jpg
 
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