Ra-100

gaffer · 20th July 2010, 04:34 PM

I am looking for info on building an integrated tube amplifier with off the shelf components, to used in the build. I have been told to look out for the RA-100 as any one any info on this amp?

Stixx · 20th July 2010, 05:16 PM

Google

http://dogstar.dantimax.dk/tubestuf/ampindex.htm

DigitalJunkie · 20th July 2010, 05:45 PM

I've got one built up from the parts that Fred had left behind,I guess he was planning to build a second "RA-100a" version. I have moved house since building it and haven't had time to pull it out in a while. I still need to set up a proper bench too.

EH EL34's at +600V?
RA-100 Amp pictures by Nothing40 - Photobucket

If you're interested,I can help you out with some of the parts I used,etc. I think I still have a few of the PCB's left also.

One suggestion would be to use a lower voltage power transformer,as you can see the B+ voltage is rather high! ~640Volts in my case.
A while back I had asked Edcor for a quote on a custom power transformer,and it was very reasonable(~$120,IIRC),so I think I'll probably go that route eventually.

One other note,with such a high B+ voltage I had to change the +230V regulator a little. I replaced the bipolar transistor(It was right on the ragged edge of SOA.) with a high voltage FET,and increased the value of the resistor on the zener chain.The zeners would drift as they heated up,and lowering the current through them helped cool them off and keep the voltage more stable.
I changed the pass transistor on the negative (-590V) rail also..I don't remember the part number offhand.The NTE38 that Fred used was hard to find,so I sub'ed in a suitable transistor..I'll find the number if you are curious.

20th July 2010, 04:34 PM	#1
gaffer diyAudio Member Join Date: Jul 2010 Location: At the moment I am live in New York Blog Entries: 1	Ra-100 I am looking for info on building an integrated tube amplifier with off the shelf components, to used in the build. I have been told to look out for the RA-100 as any one any info on this amp?

Thread Tools	Search this Thread
Show Printable Version Email this Page	Search this Thread: Advanced Search

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
ALESIS RA 100 - Schematics	fosforo	Solid State	8	16th March 2012 01:31 AM
Alesis RA-100 - may need a new transistor	deniss77	Solid State	24	3rd April 2010 09:54 PM
Schematic for Alesis RA-100... Ha! Alesis doesn't have it!!	crispycircuit	Solid State	0	22nd February 2010 09:16 PM
schematics of Rotel RA-971mk11 / RA-971	digitaldiablo	Solid State	0	12th June 2003 04:03 PM

New To Site?	Need Help?
Register to Participate Search Privacy Statement Contact Us	Frequently Asked Questions Did you forget your password? Mark Forums Read

20th July 2010, 05:16 PM	#2
Stixx diyAudio Member Join Date: Sep 2003 Location: Southern Germany	Google http://dogstar.dantimax.dk/tubestuf/ampindex.htm

20th July 2010, 05:45 PM	#3
DigitalJunkie diyAudio Member Join Date: Apr 2003 Location: Portland,Oregon Blog Entries: 4	I've got one built up from the parts that Fred had left behind,I guess he was planning to build a second "RA-100a" version. I have moved house since building it and haven't had time to pull it out in a while. I still need to set up a proper bench too. EH EL34's at +600V? RA-100 Amp pictures by Nothing40 - Photobucket If you're interested,I can help you out with some of the parts I used,etc. I think I still have a few of the PCB's left also. One suggestion would be to use a lower voltage power transformer,as you can see the B+ voltage is rather high! ~640Volts in my case. A while back I had asked Edcor for a quote on a custom power transformer,and it was very reasonable(~$120,IIRC),so I think I'll probably go that route eventually. One other note,with such a high B+ voltage I had to change the +230V regulator a little. I replaced the bipolar transistor(It was right on the ragged edge of SOA.) with a high voltage FET,and increased the value of the resistor on the zener chain.The zeners would drift as they heated up,and lowering the current through them helped cool them off and keep the voltage more stable. I changed the pass transistor on the negative (-590V) rail also..I don't remember the part number offhand.The NTE38 that Fred used was hard to find,so I sub'ed in a suitable transistor..I'll find the number if you are curious.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)