Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

How to convert PP RCA 30w to triode mode
How to convert PP RCA 30w to triode mode
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 6th December 2018, 02:06 PM   #21
20to20 is offline 20to20  United States
diyAudio Member
 
Join Date: Jun 2010
Location: W-S, NC
Quote:
Originally Posted by DF96 View Post
You need to think about ratios rather than absolute values.

The resistor is low in value because the feedback injection point resistor is also low in value. It is the ratio of these two (27) which sets the feedback; 27 is a perfectly normal feedback ratio; many amps are in the region of 30 for this figure.
This 30W amp circuit is in the RCA manual. On the next page is a 50W amp. It uses the same cathode resistors on the VA with a 10R to ground. The FB resistor is 1200R. What's the ratio for that? Both are on the 16R tap. There is no common ratio to use generally. There are many design considerations for feedback component values.

Last edited by 20to20; 6th December 2018 at 02:20 PM.
  Reply With Quote
Old 6th December 2018, 03:02 PM   #22
DF96 is offline DF96  England
diyAudio Member
 
Join Date: May 2007
1200/10=120. Generally, higher power amps use higher ratios here because they need to generate more output voltage from the same input. A voltage gain of x30 (30dB) is typical for medium power domestic amps nowadays; more gain was common 60 years ago.

Anyway, my main point is that 270 is not unusually low in value, as 27 is not an unusual feedback ratio. Hence 0.01uF is not unusually high in value. Ratios are what matter.
  Reply With Quote
Old 6th December 2018, 04:33 PM   #23
kissabout2002 is offline kissabout2002  Italy
diyAudio Member
 
Join Date: Sep 2018
Location: Philippines
Quote:
Originally Posted by 20to20 View Post
If it was a loud buzzing squeal, that sound happens when the polarity of the FB is backward. You can reverse swap the plate leads to the OPT or you can change the grounded speaker terminal to the other (+) side. That will reverse the FB polarity.
I just did it and now is working perfectly, I check also older Rca schematic and on the 30w amp the value of 0.01 uF and 270r are constant, I just have to use a 330r instead because I do not have 270r, and work very well, I swap the plate leads to the OPT rather the speaker terminal because my OPT have 4,8 and 16 ohm, I will do a proper measurement soon, still thank you very much you really solve a big problem, since I built the amp and take off the FB was working well actually very powerful but with some hum and noise problem, not to much but they was bother me, but now is absolutely silent even at the max volume, so very happy with it, I will try later to apply suggestions from other members on triode mode....thanks again
  Reply With Quote
Old 6th December 2018, 04:55 PM   #24
20to20 is offline 20to20  United States
diyAudio Member
 
Join Date: Jun 2010
Location: W-S, NC
Quote:
Originally Posted by kissabout2002 View Post
I just did it and now is working perfectly, ....thanks again
Muy bueno! Thanks for the followup.
  Reply With Quote
Old 6th December 2018, 08:18 PM   #25
Wavebourn is offline Wavebourn  United States
Designer & Technologist
diyAudio Member
 
Wavebourn's Avatar
 
Join Date: Sep 2006
Location: Pleasant Hill, CA
How to convert PP RCA 30w to triode mode
RCA engineers were creative. I like servo to the screen grid. I thought it was my invention, because I did not see that before.
__________________
Nothing in the universe is perfect. The ideal things are the ones that are most optimal. Optimization criteria, what matters. When I hear "No Compromise Design", I want to take a sledgehammer and test how impact-proof it is.
  Reply With Quote
Old 6th December 2018, 08:55 PM   #26
20to20 is offline 20to20  United States
diyAudio Member
 
Join Date: Jun 2010
Location: W-S, NC
Great minds think alike...
  Reply With Quote

Reply


How to convert PP RCA 30w to triode modeHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Luxman MB-3045: Convert from Triode (KT88 sort of) to 300B Push-pull? richp4003 Tubes / Valves 8 28th May 2018 11:31 PM
865 in triode mode...anyone ever tried it? aldovan Tubes / Valves 0 6th December 2012 12:44 AM
What is a simply way to convert the Sony CDP-555ESD in non oversampling mode? lorcoll Digital Source 1 11th November 2010 04:56 AM
Using a spdt switch to select between triode mode and pentode mode on a guitar amp. G Instruments and Amps 19 15th March 2006 10:15 AM
Mullard 5-20 in triode mode icebear Tubes / Valves 15 26th November 2004 03:06 AM


New To Site? Need Help?

All times are GMT. The time now is 11:57 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki