from the archive - Paramour 1 45 conversion

[Doc B.]

from PJ:

I have for some time wanted to try a pair of 45s in a Paramour. Been too busy with other projects so far to do more than the basic design. But it's quite easy:

Replace the 270 ohm power supply resistor with 1600 ohms 10 watts, making sure it is clear of other parts as it will dissipate quite a lot of heat. This will reduce the plate voltage to something more appropriate to the 45.

Replace the 1200 ohm cathode resistor with 1600 ohms 10 watts. This will optimize the plate current for the 45 with 4k ohm load, and reduce plate dissipation to the 10 watt rating of the 45.

[strhd07]

First, I apologize, since I'm technically clueless (known as TCB: technically clueless Bottlehead), but I'll try to pass on the question I need to ask.

I have a pair of the Paramour I amps built by someone else with the C4S and cap and iron upgrades. I took them to a local tech to convert for use with 45s. He tells me that the 270 ohm power-supply resistor isn't there (he thinks because of the addition of the choke) and wonders whether the value of the other resistor needs to be different from what I found here:

"Replace the 270 ohm power supply resistor with 1600 ohms 10 watts, making sure it is clear of other parts as it will dissipate quite a lot of heat. This will reduce the plate voltage to something more appropriate to the 45.
Replace the 1200 ohm cathode resistor with 1600 ohms 10 watts. This will optimize the plate current for the 45 with 4k ohm load, and reduce plate dissipation to the 10 watt rating of the 45."

Whether the value of the second resistor remains 1600 or should be some new value, he wonders whether anything else needs to done differently if just the one resistor is sufficient.

Please direct me if there is info somewhere that explains what needs to be done with Paramour I's that already have the C4S, cap, and iron upgrades. Best possible help would be if there's someone out there who could answer additional questions if they arise.

Thanks,

Mark, TCB

[Doc B.]

Your question is quite coherent and well put. However if your tech can't figure out what to do from the information given and he is charging you for the work I would be disinclined to have him do the work. He should have measured the DCR of the choke, found that it is 270 ohms just like the resistor it replaced, and decide to either remove the choke and replace it with the recommended 1600 ohm 10W resistor, or leave the choke in and add a 1330 ohm 10W resistor in series with it.

Aside from the above change and the change of the cathode resistor from 1200 ohms to 1600ohms there are no other changes necessary to run a 45 tube in an amp with the C4S and cap and iron upgrades.

[Grainger49]

I will be very interested in hearing your impressions of your 45 converted Paramour.  It, your Paramour, sounds much like mine and I have long wanted a 45 amp.  My only problem is whether my speakers want a 45 amp.

[strhd07]

Many thanks, Doc. I've already heard back from the tech, and he wants to know where a 10w 1330 ohm resistor can be found. I Googled a bit and see 133 ohm/10w but not 1330. Are they an exotic?

I feel a bit like Alice drinking the bottle that made her smaller. I'm going from 3.5 to 1.5 watts with the 45s, and I'm waiting for a wee 1626 amp, with a bruising .75 watts, to make an appearance.

To Grainger49, see whether you can get hold of one of the original TDS Audiophile Passive doohickeys (not the cheapo plastic AR job). It seems very transparent to me and gives a luffly 3dB boost to the signal. Might be enough to make you 45 approved. In a medium-small room, I have another 45 amp doing righteously with an old pair of Merlin VSMs, 89db, if you can believe it. Just don't look to bang no noggins or rattle the windowpanes.

Mark

[Doc B.]

One could just make a 1330 ohm up out of smaller values, say a 1200 ohm and one of those 133s you mention, wired in series.

[Paul Birkeland]

Replace the Triad C7X choke with a Hammond 157L in each amplifier.  Use a 1200 ohm 10 watt resistor in series with the 157L and you will be close enough for government work.  I would add a 27-100uf capacitor (450v rating at least) at the junction between the choke and resistor. 

The 157L has 40% more inductance than the C7X, and roughly 400 ohms of resistance, so with an easy to find 1200 ohm resistor, you will be set.  (Digikey has at least 6 different 10-15 watt 1.2k resistors available)

[Grainger49]

 .  .  .   To Grainger49, see whether you can get hold of one of the original TDS Audiophile Passive doohickeys (not the cheapo plastic AR job). It seems very transparent to me and gives a luffly 3dB boost to the signal. Might be enough to make you 45 approved. In a medium-small room, I have another 45 amp doing righteously with an old pair of Merlin VSMs, 89db, if you can believe it. Just don't look to bang no noggins or rattle the windowpanes.

Mark

Mark,

I don't rattle window panes, I listen to a lot of Bluegrass.  But I'm completely lost on getting 3dB of gain from the doohickey.  I'm also not sure anything will make my speakers more efficient.  They are 94BW already and I might be within striking range of 45 output tubes.

[Paul Joppa]

Use 1300 ohms, that's plenty close enough. The Yageo brand is cheap, tough and works fine in power supplies. Digi-Key has 545 of them in stock at $0.49 each. Mouser seems to have dropped the similar product for Xicon.

[strhd07]

Thanks to all who replied. Helped a lot.

Mark