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In Reply to: RE: Shunt Reguated 45 upgrade kit interest posted by Doc B. on June 05, 2007 at 10:20:04
Paul sent this to me yesterday - a harvest of various Paramour 45 conversion schemes including a rough guide to wiring changes for a PII upgrade to SR45 -
Non-shunt regulated 45 conversions:
To replace the 2A3 with a Type 45 tube in the Paramour, two changes are needed. The plate voltage must be reduced, and the cathode bias resistor must be increased.
For the Paramour II, these changes are documented in the manual. For the iron upgrade, they are documented in the installation instructions posted on the web site.
For the older Paramour, here are the changes:
Cathode bias resistor
The cathode bias resistor is changed from 1200 ohms to 1600 ohms.
High voltage power supply
In all cases, it is worthwhile to connect the signal ground to chassis ground. Run a short piece of wire from B1, B2, or B3 to the center tab of the 5-tab terminal strip at the driver socket – this is the T-strip that was added for the C4S upgrade. If you have the iron upgrade, don't solder the terminal strip end yet...
For the stock iron, the rest is simple – just replace the 270 ohm 5 watt resistor in the power supply with 1600 ohms, 10 watts.
If you have done the iron upgrade, and have already replaced the 270 ohm 5 watt resistor with the former plate choke (10 henry, 270 ohms DC) then you will need to add another 1300 ohms 10 watt resistor and a 47uF/450v capacitor. Disconnect the plate choke wire from T15, and re-attach it to the empty second terminal on the driver T-strip – the one between the end used by the C4S and the middle terminal, which is now ground. Don't solder yet, there are two more things to go here! Now run a 1300 ohm 10 watt resistor from T15 to this second terminal – it will parallel the 15K that goes to the C4S, but connects to the adjacent terminal. Now add a 47uF/450v cap, with the positive lead to the second T-strip terminal and the negative lead to the middle terminal. Solder both terminals.
Shunt regulated 45 conversions
To replace the 2A3 with a shunt-regulated Type 45 tube in the Paramour, you must have the current PT-2 power transformer, not the older Hammond one. The new one has solder terminals, the Hammond has leads with colored insulation.
The 45 operates at a lower plate voltage and a higher current than in the stock 45 version of Paramour, so the voltages and resistances are not the same. This article only covers conversion from 2A3 to shunt-regulated 45 operation.
Cathode bias resistor
The cathode bias resistor is changed from 1200 ohms to 1300 ohms.
High voltage power supply
The high voltage power supply remains the same. Check the voltage, which should be around 380v at T15. If it's less than 340v, the shunt regulator voltage will have to be reduced to allow some compliance for the upper current source – asking fro help on the Bottlehead forum is the main resource if you can't figure it out yourself. If it's more than 380v, then a larger heat sink may be needed – again, ask on the forum if you need help.
Shunt regulated driver
These are merely sketchy notes.
Basically, you will rip out all the driver socket connections and re-do it like the shunt-reg mod described for the Paramour II.
The input from the RCA jack goes to pin 7 of the new 6CM7 driver, through a 220 ohm carbon comp grid stopper resistor; the 249K or 270K grid leak at the RCA remains in place.
The 6v heater supply goes to B4 and B5, with the center tap to ground at or near the B socket.
The power supply positive is at T15 and goes to the shunt reg board.
The driver output is at B6, and goes to T17.
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