Bottlehead Forum

Bottlehead Kits => Legacy Kit Products => Foreplay III => Topic started by: richmi on January 01, 2015, 08:27:22 AM

Title: Retrofitting Extended Foreplay to stock. [solved]
Post by: richmi on January 01, 2015, 08:27:22 AM

Hello all,

The centre board of my Extended Foreplay died. It has been hot in there: the board has turned brown in the middle around the 68K ohm 2 watt resistors and the MJE350's metal surface were brown too. The Foreplay was connected in a Variac set at 119 volts.

So at this moment, the fastest way to have music is to revert to the stock configuration, however with 6SN7 tubes. I do not have a spare preamp.

My question is: can I use two 0.1 ohm resistors in series to get close to 0.22 ohms needed in the heater supply for 2 6SN7 tubes that require 1.2 amp current, or is it not the way it works? I mean, will these two resistors in series do the same as a single resistor wrt current? I could not find any information on the Web about this (or I was not persistent enough).

Any advice is welcome. Thanks in advance.

Richard

Title: Re: Retrofitting Extended Foreplay to stock.
Post by: Paul Birkeland on January 01, 2015, 08:39:11 AM

Hello Richard,

To very quickly get back to listening to music, move the red wire going into each "I" pad on the center board, and tack them to the "O" pad next door.  This will bypass the regulator completely, and get you back up and running.

Though we don't stock the exact parts anymore for the Extended FP-III center regulator board, I can build you a replacement when I'm back in the office.

-PB

Title: Re: Retrofitting Extended Foreplay to stock.
Post by: richmi on January 01, 2015, 09:53:54 AM

Hi PB,

I took the board apart yesterday, cleaned and rebuilt it with two MJE5731As (flipped) and checked for continuity as much as I could all along to rule out this possibility. I checked all the resistors (all good), but could not check the transistors. These were difficult to remove and I do not know if I could have ruined them. Some of the traces are damaged, so it is possible that there is a bad contact somwhere. All this to no avail.

I had made a list of the required parts to build the board again and I was thinking of hardwiring it.

Your offer makes more sense. Let me know how to proceed and the cost of it.

I will try what you suggest later today, hoping it will work.

Thanks a lot for your help.

Richard

Title: Re: Retrofitting Extended Foreplay to stock.
Post by: galyons on January 01, 2015, 09:55:11 AM

PB,
Thanks for the directions to get the FP3X at least playing.  My center board is also pretty much toast around the MJE350's.  I had replaced the MJE350's just over  year ago, but the the board was pretty "iffy" at the time.  If you have a replacement board and parts, (I have MJE350's and HLMP6000's),  I would love to get them.  Or, do you think it better to go to  MJE5731A's? I can solder it up.  It would be great to get  the FP3X reliable again!!

Happy New Year,
Geary

Title: Re: Retrofitting Extended Foreplay to stock.
Post by: Paul Birkeland on January 01, 2015, 10:14:44 AM

I don't really recommend reworking the boards, as it can take a lot of heat to get everything apart, and some of those small traces will want to lift, especially on a board that's had a few years of cooking.

When I produce a new center board, I use the MJE5731A and PN2907 transistors.  A couple of the resistors are also slightly different, as our inventory has changed a bit since the Extended Foreplay kit was discontinued.

-PB

Title: Re: Retrofitting Extended Foreplay to stock.
Post by: richmi on January 14, 2015, 09:05:39 AM

Hello again,

The new centre board arrived today.

Installed it; all the voltages are spot on.

And it works!

Thanks PB and Eileen!

Richard